Hydrophobic cross-linked gels for bioabsorbable drug carrier coatings

ABSTRACT

Coatings for medical devices, methods of making the coatings, and methods of using them are described.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/727,312, filed on Oct. 15, 2005, the entire contents ofwhich are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Vascular procedures, such as vascular reperfusion procedures, balloonangioplasty, and mechanical stent deployment, can often result invascular injury following mechanical dilation and luminal expansion of anarrowed vessel. Often, subsequent to such intravascular procedures,neointimal proliferation and vascular injury remodeling occurs along theluminal surface of the injured blood vessel; more specifically,remodeling occurs in the heart, as well as in vulnerable peripheralblood vessels like the carotid artery, iliac artery, femoral andpopliteal arteries. No known mechanical suppression means has been foundto prevent or suppress such cellular proliferation from occurringimmediately following vascular injury from mechanical reperfusionprocedures. Left untreated, restenosis within the vessel lumen withinweeks of a vascular injury can occur. Restenosis results in re-narrowingof the vessel lumen, causing massive fibrin and platelet deposition anduncontrolled cellular remodeling, which leads to restricted blood flowand thrombosis of the luminal surface. Restenosis pre-disposes thepatient to a totally occluded and/or critical ischemic event withmorbidity.

Restenosis initiated by vascular injury cellular remodeling can be agradual process. Multiple processes, including fibrin and plateletdeposition, luminal thrombosis, inflammation, calcineurin activation,growth factor and cytokine release, cell proliferation, cell migrationand extracellular matrix synthesis each contribute to the restenoticprocess. While the exact mechanism of restenosis is not completelyunderstood, several suspected biochemical pathways involved in cellinflammation, growth factor stimulation and fibrin and plateletdeposition have been postulated. Cell derived growth factors such asplatelet derived growth factor, fibroblast growth factor, epidermalgrowth factor, thrombin, etc., released from platelets, invadingmacrophages and/or leukocytes, or directly from the smooth muscle cells,provoke proliferative and migratory responses in medial smooth musclecells. These cells undergo a change from the contractile phenotype to asynthetic phenotype. Proliferation/migration usually begins within oneto two days post-injury and peaks several days thereafter. In the normalarterial wall, smooth muscle cells proliferate at a low rate,approximately less than 0.1 percent per day.

However, daughter cells migrate to the intimal layer of arterial smoothmuscle and continue to proliferate and secrete significant amounts ofextracellular matrix proteins. Proliferation, migration andextracellular matrix synthesis continue until the damaged endotheliallayer is repaired, at which time proliferation slows within the intima,usually within seven to fourteen days post-injury. The newly formedtissue is called neointima. The further vascular narrowing that occursover the next three to six months is due primarily to negative orconstrictive remodeling.

Simultaneous with local proliferation and migration, inflammatory cellsderived from the medial layer of the vessel wall continually invade andproliferate at the site of vascular injury as part of the healingprocess. Within three to seven days post-injury, substantialinflammatory cell formation and migration have begun to accumulate alongthe vessel wall to obscure and heal over the site of the vascularinjury. In animal models, employing either balloon injury or stentimplantation, inflammatory cells may persist at the site of vascularinjury for at least thirty days. Inflammatory cells may contribute toboth the acute and protracted chronic phases of restenosis andthrombosis.

Today, a preferred approach to the local delivery of a drug to the siteof vascular injury caused by an intravascular medical device, such as acoronary stent, is to place a drug eluting coating on the device.Clinically, medical devices coated with a drug eluting coating comprisedof either a permanent polymer or degradable polymer and an appropriatetherapeutic agent, have shown angiographic evidence that vascular wallproliferation following vascular injury and/or vascular reperfusionprocedures can be reduced if not eliminated for a certain period of timesubsequent to balloon angioplasty and/or mechanical stent deployment.Local delivery of a single sirolimus or taxol compound via a drugeluting medical device has been shown to be effective at minimizing orpreventing cellular proliferation and cellular remodeling when appliedimmediately after vascular injury. Various analogs of these twoanti-proliferative compound examples have also been shown experimentallyand clinically to exhibit similar anti-proliferative activity withsimilar drug eluting coatings. However, anti-proliferative compoundssuch as sirolimus and taxol, together with a polymeric drug elutingcoating have also been shown clinically to exhibit a number of toxicside effects, during and after principal drug release from the drugeluting coating. These chronic and or protracted side effects placelimits on the amount of drug that can actually be delivered over a givenperiod of time, as well as challenge the compatibility of the polymercoatings used to deliver a therapeutic agent locally to the site of thevascular injury when applied directly to a site of inflammation and orcellular remodeling. In addition, local overdosage of compound likesirolimus and taxol can prevent, limit or even stop cellular remodelingor proliferation in and around the localized tissue area of the medicaldevice. For example, a lack of endothelial cell coverage during theinterruption of cell proliferation thought the vascular injury healingprocess exhibits a high potential for luminal thrombosis whereby fibrinand a constant deposition of platelets blanket the exposed andnon-healed medical device and/or damaged vascular injury. Withoutuninterrupted systemic support or administration of an anti-plateletmedication like clopidegrel combined with an anti-clotting agent, suchas ASA, prior to and following deployment of a drug eluting medicaldevice, such devices have been shown clinically to thrombose and occludewithin days of deployment. In addition, although these commerciallyavailable drug eluting polymer coatings employed on medical devices aregenerally characterized as being biocompatible, the lack of chemicalbreakdown, degradation and absorption of these polymer-based chemistriesinto smaller, easier to metabolize chemical components or products havebeen now been clinically demonstrated to initiate a protracted localizedinflammatory response at the site of the vascular injury, which may leadto unexpected thromobotic occlusion within days of stoppinganti-platelet medication.

Wound healing or response to in-vivo injury follows the same generalbiological cascade as in vascular injury. Namely, inflammation of nativetissue followed by migration and proliferation of cells to mitigate theinflammatory response; including platelets and macrophages; andsubsequent healing phase which includes fibrin deposition and tissueremodeling.

The sustained nature of the thrombotic and inflammatory response toinjury makes it desirable to provide localized drug delivery coatingsthat can release the one or more therapeutic agents over a period oftime in order to minimize such cell activated response, and to reducethe potential toxic side effects of many drugs makes it desirable toprovide alternative non-polymeric, bioabsorbable carrier that deliversthe drug via a bioabsorbable mechanism.

SUMMARY OF THE INVENTION

What is desired is a drug delivery coating that can release and delivera therapeutic agent in a sustained and preferably controlled fashion tothe local tissue, without chronic inflammation due to either thetherapeutic agent or break-down products of the coating. The presentinvention is directed toward various solutions that facilitateaddressing this need.

What is also desired is a coating that can be bioabsorbed by cells andthat can deliver a drug without inducing chronic localized inflammationto tissues (e.g., vascular tissue) that has been injured mechanically orby reperfusion injury, whereby the coating and the therapeutic agent areingested and metabolized by the cell, as it consumes the breakdownproducts of the coating with the drug.

In various aspects, the present inventions provide methods for producinghydrophobic, non-polymeric cross-linked gel coatings comprising one ormore therapeutic agents that facilitate the controlled loading of theone or more of therapeutic agent, sustained release of a therapeuticagent, and controlled release of a therapeutic agent the coating isingested and absorbed. In various embodiments, provided are methods oftailoring the drug release profile of a hydrophobic, non-polymericcross-linked gel by control of the curing conditions used to produce thecross-linked gel from a natural oil containing starting material; theuse of a free radical scavenger in a natural oil containing startingmaterial from which the gel is formed, or combinations thereof. Invarious embodiments, the methods of the present invention tailor thedrug release properties of a hydrophobic, non-polymeric cross-linked gelcoating by controlling the degree of cross-linking in the gel. Invarious embodiments, the methods of the present invention tailor thedrug delivery properties of a hydrophobic, non-polymeric cross-linkedgel coating by controlling the level of fatty acids, tocopherols andsoluble components in the cross-linked gel.

In various aspects, the present inventions provide hydrophobic,non-polymeric cross-linked gel coatings comprising one or moretherapeutic agents with a tailored release profile for one or more ofthe therapeutic agents. In various embodiments, the tailored releaseprofile comprises a sustained release profile. In various embodiments,the tailored release profile properties are controlled by the level offatty acids, tocopherols and soluble components in the cross-linked gel.In various aspects of the present invention, the bio-absorbablecross-linked gel contains fatty acids, many of which originate astriglycerides. It has previously been demonstrated that triglyceridebyproducts, such as partially hydrolyzed triglycerides and fatty acidmolecules can integrate into cellular membranes and enhance thesolubility of drugs into the cell. Whole triglycerides are known not toenhance cellular uptake as well as partially hydrolyzed triglyceride,because it is difficult for whole triglycerides to cross cell membranesdue to their relatively larger molecular size. Vitamin E compounds canalso integrate into cellular membranes resulting in decreased membranefluidity and cellular uptake.

In various aspects, the present inventions provide a hydrophobic crosslinked gel containing fatty acids and alpha-tocopherol in differingamounts and ratios to contribute to a cross-linked gel in a manner thatprovides control over the cellular uptake characteristics of thecross-linked gel and any therapeutic agents mixed therein.

In various aspects, the present inventions provide coated medicaldevices having a non-polymeric bio-absorbable drug release coatingcomprising one or more layers of hydrophobic cross-linked gel, whereinat least one of the cross-linked gel layers contains one or moretherapeutic agents. In various embodiments, the drug release coatingdoes not substantially decompose, in vivo, into either lactic acids orglycolic acid compounds. In various embodiments, the drug releasecoating hydrolyzes in vivo, into substantially non-inflammatorycompounds. In various embodiments, the coated medical device isimplantable in a patient to effect long term local delivery of thetherapeutic agent to the patient. In various embodiments the delivery isat least partially characterized by the total and relative amounts ofthe therapeutic agent released over time. In various embodiments, thetailored delivery profile is controlled by the level of solublecomponents in the cross-linked gel. In various embodiments, the deliveryprofile is a function of the solubility and lipophilicity of the coatingcomponents and therapeutic agent in-vivo.

In various embodiments, the present inventions provide coatings wherethe drug release profile of the coating is tailored through theprovision of two or more coatings and selection of the location of thetherapeutic agent. The drug location can be altered, e.g., by coating abare portion of a medical device with a first starting material andcreating a first cured coating, then coating at least a portion of thefirst cured-coating with the drug-oil formulation to create a secondoverlayer coating. The first starting material can comprise one or moretherapeutic agents. In various embodiments, the second overlayer coatingis also cured. The drug load, drug release profiles and/or drug deliveryof the first coating, the overlay coating, or both, can be tailoredthrough the use of different curing conditions and/or addition of freeradical scavengers (e.g., vitamin E), as described herein.

It is to be understood that the process of providing two layers, can beextended to provide three or more layers, wherein at least one of thelayers comprises a hydrophobic, non-polymeric cross-linked gel. Inaddition, one or more of the layers can be drug releasing, and the drugrelease profile of such layers can be tailored using the methodsdescribed herein.

In accordance with various embodiments of the present invention, thehydrophobic, non-polymeric, cross-linked gel contains lipids. Thehydrophobic cross-linked gel is formed from a naturally occurring oil,such as fish oil, starting material. The hydrophobic cross-linked gelcan contain omega-3 fatty acids. The hydrophobic cross-linked gel canalso contain alpha-tocopherol or vitamin E.

The coatings of the present invention can be formulated to contain avariety of other chemicals and entities in addition to a therapeuticagent, including, but not limited to, one or more of: a pharmaceuticallyacceptable carrier, an excipient, a surfactant, a binding agent, anadjuvant agent, and/or a stabilizing agent (including preservatives,buffers and antioxidants). In one embodiment, alpha-tocopherol TPGS maybe added to the coatings of the present invention.

In various aspects, the present inventions provide methods for treatinginjury in a mammal, such as, e.g., a human. In various embodiments, theinjury is a vascular injury. In various embodiments, the methodscomprise locally administering one or more therapeutic agents in atherapeutically effective amount by sustained release of the one or moretherapeutic agents from a coating comprising a hydrophobic,non-polymeric cross-linked gel.

The teachings herein demonstrate that cured fish oil soft tissue meshcoatings can allow for the ability to regulate the release profile ofdrug-loaded fish oil-based coatings from implantable devices. In variousembodiments, the release profile can be controlled through changes inoil coating chemistry by varying coating composition and cure times. Theteachings demonstrate that hydrophobic, non-polymeric cross-linked gelsproduced by 150° F. curing for 3 days possess lessperoxide/ether/carbon-carbon cross-links than those cured at 200° F.curing for 24 hours. The teachings demonstrate that the cross-linkingand gelation of the cured fish oil coatings can be directly dependent onthe formation of hydroperoxides in the fish oil component, whichincreases with increasing temperature. Dissolution experiments presentedherein have shown that drug release and coating degradation are morerapid for the cross-linked coatings produced using 150° F. curingconditions as compared to those created employing the 200° F. curingconditions.

The teachings herein demonstrate that the use of vitamin E in cured fishoil coatings is another method to alter the cross-linking and drugrelease properties of the coating. Vitamin E is an antioxidant that canslow down autoxidation in fish oil by reducing, it is believed,hydroperoxide formation during curing. This can result in a decrease inthe amount of cross-linking observed in a cured fish oil coating.Increasing the amount of vitamin E in the coating can result inlengthening and slowing the release of a therapeutic agent from thecoating. For example, the teachings herein demonstrate a lengthening andslowing of the release of the rapamycin, from a hydrophobic,non-polymeric cross-linked gel coating into a dissolution buffer, due,it is believed, to rapamycin's affinity for the fatty acid and vitamin Ecomponents in the cured fish oil coating. The teachings herein furtherindicate that vitamin E can also results in protecting a drug such asrapamycin and increase the amount of such drug extracted from thecoating.

In another aspect, the invention provides a hydrophobic, non-polymericcross-linked gel comprising a therapeutic agent cross linked to a fattyacid. In one embodiment, the fatty acid is an omega 3-fatty acid. Inanother embodiment, the therapeutic agent comprises a group capable ofbeing cross linked. In still another embodiment, the therapeutic agentcomprises an unsaturation. In still another embodiment, the therapeuticagent is rapamycin. In another embodiment of the gel, the gel comprisesfish oil. In another embodiment, the invention provides a coatingcomprising the hydrophobic, non-polymeric cross-linked gel describedherein. In another embodiment, the invention provides a medical devicecomprising the hydrophobic, non-polymeric cross-linked gel describedherein.

The teachings herein also demonstrate that the positioning of thedrug-containing layer on a coated medical device can alter the releaseprofile of the coating.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects, embodiments, objects, features andadvantages of the invention can be more fully understood from thefollowing description in conjunction with the accompanying drawings. Inthe drawings, like reference characters generally refer to like featuresand structural elements throughout the various figures. The drawings arenot necessarily to scale, emphasis instead being placed uponillustrating the principles of the invention.

FIG. 1 is a schematic illustration of an example of the creation ofperoxide and ether cross-linking in a polyunsaturated oil;

FIG. 2 is a schematic illustration of an example of the creationcarbon-carbon cross-linking in a polyunsaturated oil (Diels-Alder typereaction);

FIG. 3 schematically depicts the hydrolysis of the ester links in atrygliceride;

FIG. 4 is a flow chart illustrating a method of making the coatedmedical device of the present invention, in accordance with oneembodiment of the present invention;

FIG. 5 is a flow chart illustrating a variation of the method of FIG. 4,in accordance with one embodiment of the present invention;

FIGS. 6A-6C are various images of coated medical devices;

FIG. 7 schematically depicts various chemical structures of the fattyacid chains that were detected after saponification of the cured fishoil coating of Example 1;

FIG. 8 depicts a FTIR analysis of the final cured coating after heatingat 200° F. for 24 hr of Example 1;

FIGS. 9A-9C depict analysis of FTIR data discussed in Example 1;

FIGS. 10A-C are an FTIR spectra comparison of the coating cured at 150°F. for 3 days and the coating cured at 200° F. for 24 hours;

FIG. 11A depicts a DSC curve of the soluble materials in the cured fishoil coating of Example 1;

FIG. 11B depicts a DSC curve of the insoluble materials in the curedfish oil coating of Example 1;

FIG. 12 schematically depicts the molecular structures of the componentsdetected in the soluble fraction of the coating of Example 1;

FIG. 13 depicts a representative FTIR spectrum of the cured coatinghydrolyzed in buffer solution consistent with the production of fattyacid, fatty acid salts, and alcohols at day 16 as discussed in Example1;

FIG. 14 schematically depicts the production of a hydrophobic,non-polymeric cross-linked gel of Example 1;

FIGS. 15 and 16 depict drug release data in an aqueous media discussedin Example 2;

FIG. 17 depicts FTIR data discussed in Example 3;

FIG. 18 depicts drug release data in an aqueous media discussed inExample 3;

FIGS. 19-23 depict drug release data in an aqueous media discussed inExample 4;

FIGS. 24A-B and depict 25A-B an FTIR comparison analysis of a heat curedencapsulated mesh coating and a UV and heat cured film coating;

FIGS. 26A-C depict curves illustrating the release of a rapamycincompound in an aqueous media from the coating over time;

FIG. 27 depicts the percent inhibition of cell growth based on theconcentration of rapamycin released from the coating;

FIGS. 28A-D depict FTIR data discussed in Example 7; and

FIG. 29 depicts an analysis of the FTIR data discussed in Example 7.

DETAILED DESCRIPTION

The present inventions are directed towards coatings for medical devicesfor release and local delivery of one or more therapeutic agents,methods of forming and tailoring the properties of said coatings andmethods of using said coatings for treating injury in a mammal.

Prior to further describing the invention, it may be helpful to anunderstanding thereof to generally and briefly describe injury and thebiological response thereto.

Vascular Injury

Vascular injury causing intimal thickening can be broadly categorized asbeing either biologically or mechanically induced. Biologically mediatedvascular injury includes, but is not limited to, injury attributed toinfectious disorders including endotoxins and herpes viruses, such ascytomegalovirus; metabolic disorders, such as atherosclerosis; andvascular injury resulting from hypothermia, and irradiation.Mechanically mediated vascular injury includes, but is not limited to,vascular injury caused by catheterization procedures or vascularscraping procedures, such as percutaneous transluminal coronaryangioplasty; vascular surgery; transplantation surgery; laser treatment;and other invasive procedures which disrupt the integrity of thevascular intima or endothelium. Generally, neointima formation is ahealing response to a vascular injury.

Inflammatory Response

Wound healing upon vascular injury occurs in several stages. The firststage is the inflammatory phase. The inflammatory phase is characterizedby hemostasis and inflammation. Collagen exposed during wound formationactivates the clotting cascade (both the intrinsic and extrinsicpathways), initiating the inflammatory phase. After injury to tissueoccurs, the cell membranes, damaged from the wound formation, releasethromboxane A2 and prostaglandin 2-alpha, which are potentvasoconstrictors. This initial response helps to limit hemorrhage. Aftera short period, capillary vasodilatation occurs secondary to localhistamine release, and the cells of inflammation are able to migrate tothe wound bed. The timeline for cell migration in a normal wound healingprocess is predictable. Platelets, the first response cell, releasemultiple chemokines, including epidermal growth factor (EGF),fibronectin, fibrinogen, histamine, platelet-derived growth factor(PDGF), serotonin, and von Willebrand factor. These factors helpstabilize the wound through clot formation. These mediators act tocontrol bleeding and limit the extent of injury. Platelet degranulationalso activates the complement cascade, specifically C5a, which is apotent chemoattractant for neutrophils.

As the inflammatory phase continues, more immune response cells migrateto the wound. The second response cell to migrate to the wound, theneutrophil, is responsible for debris scavenging, complement-mediatedopsonization of bacteria, and bacteria destruction via oxidative burstmechanisms (i.e., superoxide and hydrogen peroxide formation). Theneutrophils kill bacteria and decontaminate the wound from foreigndebris.

The next cells present in the wound are the leukocytes and themacrophages (monocytes). The macrophage, referred to as theorchestrator, is essential for wound healing. Numerous enzymes andcytokines are secreted by the macrophage. These include collagenases,which debride the wound; interleukins and tumor necrosis factor (TNF),which stimulate fibroblasts (produce collagen) and promote angiogenesis;and transforming growth factor (TGF), which stimulates keratinocytes.This step marks the transition into the process of tissuereconstruction, i.e., the proliferative phase.

Cell Proliferation

The second stage of wound healing is the proliferative phase.Epithelialization, angiogenesis, granulation tissue formation, andcollagen deposition are the principal steps in this anabolic portion ofwound healing. Epithelialization occurs early in wound repair. At theedges of wounds, epidermis immediately begins thickening. Marginal basalcells begin to migrate across the wound along fibrin strands stoppingwhen they contact each other (contact inhibition). Within the first 48hours after injury, the entire wound is epithelialized. Layering ofepithelialization is re-established. The depths of the wound at thispoint contain inflammatory cells and fibrin strands. Aging effects areimportant in wound healing as many, if not most, problem wounds occur inan older population. For example, cells from older patients are lesslikely to proliferate and have shorter life spans and cells from olderpatients are less responsive to cytokines.

Heart disease can be caused by a partial vascular occlusion of the bloodvessels that supply the heart, which is preceded by intimal smoothmuscle cell hyperplasia. The underlying cause of the intimal smoothmuscle cell hyperplasia is vascular smooth muscle injury and disruptionof the integrity of the endothelial lining. Intimal thickening followingarterial injury can be divided into three sequential steps: 1)initiation of smooth muscle cell proliferation following vascularinjury, 2) smooth muscle cell migration to the intima, and 3) furtherproliferation of smooth muscle cells in the intima with deposition ofmatrix. Investigations of the pathogenesis of intimal thickening haveshown that, following arterial injury, platelets, endothelial cells,macrophages and smooth muscle cells release paracrine and autocrinegrowth factors (such as platelet derived growth factor, epidermal growthfactor, insulin-like growth factor, and transforming growth factor) andcytokines that result in the smooth muscle cell proliferation andmigration. T-cells and macrophages also migrate into the neointima. Thiscascade of events is not limited to arterial injury, but also occursfollowing injury to veins and arterioles.

Granulomatous Inflammation

Chronic inflammation, or granulomatous inflammation, can cause furthercomplications during the healing of vascular injury. Granulomas areaggregates of particular types of chronic inflamatory cells which formnodules in the millimeter size range. Granulomas may be confluent,forming larger areas. Essential components of a granuloma arecollections of modified macrophages, termed epithelioid cells, usuallywith a surrounding zone of lymphocytes. Epithelioid cells are so namedby tradition because of their histological resemblance to epithelialcells, but are not in fact epithelial; they are derived from bloodmonocytes, like all macrophages. Epithelioid cells are less phagocyticthan other macrophages and appear to be modified for secretoryfunctions. The full extent of their functions is still unclear.Macrophages in granulomas are commonly further modified to formmultinucleate giant cells. These arise by fusion of epithelioidmacrophages without nuclear or cellular division forming huge singlecells which may contain dozens of nuclei. In some circumstances thenuclei are arranged round the periphery of the cell, termed aLanghans-type giant cell; in other circumstances the nuclei are randomlyscattered throughout the cytoplasm (i.e., the foreign body type of giantcell which is formed in response to the presence of other indigestibleforeign material in the tissue). Areas of granulomatous inflammationcommonly undergo necrosis.

Formation of granulomatous inflammation seems to require the presence ofindigestible foreign material (derived from bacteria or other sources)and/or a cell-mediated immune reaction against the injurious agent (typeIV hypersensitivity reaction).

Drug Release and Delivery Coatings

The coatings of the present invention comprise a hydrophobicnon-polymeric cross-linked gel, one or more therapeutic agents, and afatty acid. In a further embodiment, the coating comprises thehydrophobic non-polymeric cross-linked gel and a fatty acid, and furthercomprises one or more of the group consisting of a glyceride, aglycerol, and a fatty alcohol and also may further comprise atherapeutic agent.

The coating can comprise both soluble and insoluble components. As usedin the context of the cross-linked gel coating described herein, theterms “soluble” and “insoluble” refer the solubility of the coating in apolar solvent such as, e.g., tetrahydrofuran (THF), e.g., as determinedby gravimetric analysis. For example, the coatings may be about 60%-75%soluble in THF and about 25%-40% insoluble in THF, or alternatively, thecoatings may be about 45-55% soluble in THF and about 45-55% insolublein THF, or alternatively, the coatings may be about 30%-55% soluble inTHF and 45%-70% insoluble in THF, as determined by gravimetric analysis.Generally, at least some of the components resistant to extraction inorganic solvent (such as THF) may include cross linked components, whichmay comprise free or esterified fatty acids with chain lengths of aboutC₁₀-C₂₂.

It should be noted that the term cross-linked gel, as utilized hereinwith reference to the present invention, refers to a gel that isnon-polymeric and is derived from an oil composition comprisingmolecules covalently cross-linked into a three-dimensional network byone or more of ester, ether, peroxide, and carbon-carbon bonds in asubstantially random configuration. In various preferred embodiments,the oil composition comprises a fatty acid molecule, a glyceride, andcombinations thereof.

In addition, the hydrophobic non-polymeric cross-linked gel coatings ofthe present invention are bioabsorbable as described herein. Thetherapeutic agent can be an active agent as contained in the coatingand/or a prodrug that, e.g., becomes active once released from thecoating. The coating may be selected such that it delivers or releasesthe therapeutic agent at a desired rate and/or therapeutically effectiverate in vivo. In another embodiment, the coating may have an averagedrug loading of about 1-50% by weight.

The hydrophobic non-polymeric cross-linked gel coatings of the presentinventions are formed from an oil component. The term “oil component” isalso referred to herein as the “oil-containing starting material.” The“oil-containing starting material” may be natural or derived fromsynthetic sources. Preferably, the “oil containing starting material”comprises unsaturated fatty acids. The oil component can be either anoil, or an oil composition. The oil component can be a naturallyoccurring oil, such as fish oil, cod liver oil, cranberry oil, asynthetic oil, or other oils having desired characteristics. One exampleembodiment of the present invention makes use of a fish oil in partbecause of the high content of omega-3 fatty acids, which can providehealing support for damaged tissue, as discussed herein. The fish oilcan also serve as an anti-adhesion agent. In addition, the fish oilmaintains anti-inflammatory or non-inflammatory properties as well. Thepresent invention is not limited to formation of the hydrophobicnon-polymeric cross-linked gel coating with fish oil as the naturallyoccurring oil. However, the following description makes reference to theuse of fish oil as one example embodiment. Other naturally occurringoils or synthetic oils can be utilized in accordance with the presentinvention as described herein.

It should be noted that as utilized herein, the terms “fish oil”includes but is not limited to omega-3 fatty acid, fish oil fatty acid,free fatty acid, monoglycerides, diglycerides, or triglycerides, estersof fatty acids, or a combination thereof. The fish oil may include oneor more of arachidic acid, gadoleic acid, arachidonic acid,eicosapentaenoic acid, docosahexaenoic acid or derivatives, analogs andpharmaceutically acceptable salts thereof.

Furthermore, as utilized herein, the term free fatty acid includes butis not limited to one or more of butyric acid, caproic acid, caprylicacid, capric acid, lauric acid, myristic acid, palmitic acid,palmitoleic acid, stearic acid, oleic acid, vaccenic acid, linoleicacid, alpha-linolenic acid, gamma-linolenic acid, behenic acid, erucicacid, lignoceric acid, analogs and pharmaceutically acceptable saltsthereof. The naturally occurring oils, including fish oil, are cured asdescribed herein to form a hydrophobic cross-linked gel, creating thecoating.

With regard to the aforementioned oils, it is generally known that thegreater the degree of unsaturation in the fatty acids the lower themelting point of a fat, and the longer the hydrocarbon chain the higherthe melting point of the fat. A polyunsaturated fat, thus, has a lowermelting point, and a saturated fat has a higher melting point. Thosefats having a lower melting point are more often oils at roomtemperature. Those fats having a higher melting point are more oftenwaxes or solids at room temperature. Therefore, a fat having thephysical state of a liquid at room temperature is an oil. In general,polyunsaturated fats are liquid oils at room temperature, and saturatedfats are waxes or solids at room temperature.

Polyunsaturated fats are one of four basic types of fat derived by thebody from food. The other fats include saturated fat, as well asmonounsaturated fat and cholesterol. Polyunsaturated fats can be furthercomposed of omega-3 fatty acids and omega-6 fatty acids. Under theconvention of naming, the unsaturated fatty acid according to theposition of its first double bond of carbons, those fatty acids havingtheir first double bond at the third carbon atom from the methyl end ofthe molecule are referred to as omega-3 fatty acids. Likewise, a firstdouble bond at the sixth carbon atom is called an omega-6 fatty acid.There can be both monounsaturated and polyunsaturated omega fatty acids.

Omega-3 and omega-6 fatty acids are also known as essential fatty acidsbecause they are important for maintaining good health, despite the factthat the human body cannot make them on its own. As such, omega-3 andomega-6 fatty acids must be obtained from external sources, such asfood. Omega-3 fatty acids can be further characterized as containingeicosapentaenoic acid (EPA), docosahexanoic acid (DHA), andalpha-linolenic acid (ALA). Both EPA and DHA are known to haveanti-inflammatory effects and wound healing effects within the humanbody.

As utilized herein, the term “bio-absorbable” generally refers to havingthe property or characteristic of being able to penetrate the tissue ofa patient's body. In certain embodiments of the present inventionbio-absorption occurs through a lipophilic mechanism. The bio-absorbablesubstance can be soluble in the phospholipid bi-layer of cells of bodytissue, and therefore impact how the bio-absorbable substance penetratesinto the cells.

It should be noted that a bio-absorbable substance is different from abiodegradable substance. Biodegradable is generally defined as capableof being decomposed by biological agents, or capable of being brokendown by microorganisms or biological processes. Biodegradable substancescan cause inflammatory response due to either the parent substance orthose formed during breakdown, and they may or may not be absorbed bytissues. Some biodegradable substances are limited to bulk erosionmechanism for breakdown.

Examples of medical devices that may be coated with the coatings of theinvention include, but are not limited to, stents, catheter balloons,surgical mesh and encapsulated surgical mesh.

Drug Release and Delivery

The coatings of the present invention deliver one or more therapeuticagents locally to a targeted area using a medical device or apparatusbearing the coating at a selected targeted tissue location of thepatient that requires treatment. The therapeutic agent is transferredalong with the coating to the targeted tissue location. The combinedrelease and local delivery of a therapeutic agent enables a moreconcentrated and higher quantity of therapeutic agent via lipophiliccoating components independent of diffusion to be delivered directly atthe targeted tissue location, without having broader systemic sideeffects. With local delivery, the therapeutic agent that escapes thetargeted tissue location dilutes as it travels to the remainder of thepatient's body, substantially reducing or eliminating systemic sideeffects.

Targeted local therapeutic agent delivery using a medical device can befurther broken into two categories, namely, short term and long term.The short term delivery of a therapeutic agent occurs generally within amatter of seconds or minutes to a few days or weeks. The long termdelivery of a therapeutic agent occurs generally within weeks to months.

The phrase “sustained release” as used herein generally refers to therelease of a biologically active agent that results in the long termdelivery of the active agent.

The phrase “controlled release” as used herein generally refers to therelease of a biologically active agent in a substantially predictablemanner over the time period of weeks or months, as desired andpredetermined upon formation of the biologically active agent on themedical device from which it is being released. Controlled releaseincludes the provision of an initial burst of release upon implantation,followed by the substantially predictable release over theaforementioned time period.

Examples of therapeutic agents which may advantageously be administeredthrough sustained release include anti-proliferative andanti-inflammatory agents. These agents will be loaded into the coatingat drug loading level which may affect the rate of their release. Theamount of drug released over a particular time frame can be tailored toparticular classes of drugs, particular drugs, particular diseases andparticular subjects.

For example, for one anti-proliferative drug, the coating may have anaverage drug loading of about 500 to about 1500 micrograms per squareinch, about 600 to about 1450 micrograms per square inch, about 700 toabout 1400 micrograms per square inch, about 800 to about 1350micrograms per square inch, about 900 to about 1300 micrograms persquare inch, about 1000 to about 1300 micrograms per square inch, orabout 1100 to about 1300 micrograms per square inch (after curing).Furthermore, the coating may release the drug over a period of at leastabout 5 days, at least about 6 days, at least about 7 days, at leastabout 8 days, at least about 9 days, at least about 10 days, at leastabout 11 days, at least about 12 days, at least about 13 days, at leastabout 14 days, at least about 15 days, at least about 16 days, at leastabout 17 days, at least about 18 days, at least about 19 days, or atleast about 20 days. In a further embodiment, the coating releases thedrug over a period of about 17 to about 20 days.

For another therapeutic agent, such as an anti-proliferative drug, thecoating may have an average drug loading of about 300 to about 800micrograms per square inch after curing, about 200 to about 800micrograms per square inch, about 300 to about 700 micrograms per squareinch, about 400 to about 600 micrograms per square inch, or about 400 toabout 500 micrograms per square inch (after curing). Furthermore, thecoating may release the drug over a period of at least about 10 days, atleast about 15 days, at least about 20 days, at least about 25 days, atleast about 30 days, at least about 35 days, at least about 40 days, orat least about 45 days. In a further embodiment, the coating releasesthe drug over a period of about 35 to about 45 days.

For another therapeutic agent, such as an anti-inflammatory agent, thecoating may have an average drug loading of about 50 to about 600micrograms per square inch, about 75 to about 500 micrograms per squareinch, about 100 to about 400 micrograms per square inch, or about 150 toabout 350 micrograms per square inch (after curing). Furthermore, thecoating may release the drug over a period of at least about 5 days, atleast about 6 days, at least about 7 days, at least about 8 days, atleast about 9 days, at least about 10 days, at least about 11 days, atleast about 12 days, at least about 13 days, at least about 14 days, orat least about 15 days. In a further embodiment, the coating releasesthe drug over a period of about 10 to about 15 days.

For another therapeutic agent, such as an anti-inflammatory agent, thecoating may have an average drug loading of about 200 to about 800micrograms per square inch, about 300 to about 700 micrograms per squareinch, about 400 to about 600 micrograms per square inch, or about 400 toabout 500 micrograms per square inch (after curing). Furthermore, thecoating may release the drug over a period of at least about 10 days, atleast about 15 days, at least about 20 days, at least about 25 days, atleast about 30 days, at least about 35 days, at least about 40 days, orat least about 45 days. In a further embodiment, the coating releasesthe drug over a period of about 25 to about 30 days.

Drug Release Mechanisms

Prior attempts to create coatings, films and drug delivery platforms,such as in the field of stents, primarily make use of high molecularweight synthetic polymer based materials to provide the ability tobetter control the release of the therapeutic agent. Essentially, thepolymer in the platform releases the drug or agent via diffusion basedmechanism at a predetermined rate once implanted at a location withinthe patient. Regardless of how much of the therapeutic agent would bemost beneficial to the damaged tissue, the polymer releases thetherapeutic agent based on properties of the polymer, e.g., erosion ofthe polymeric material and drug diffusion out of the solid matrix.Accordingly, the effect of the therapeutic agent is substantially localat the surface of the tissue making contact with the medical devicehaving the coating. In some instances the effect of the therapeuticagent is further localized to the specific locations of, for example,stent struts or mesh pressed against the tissue location being treated.These prior approaches can create the potential for a concentratedlocalized toxic effect.

In various embodiments of the present inventions, the coatings releaseand deliver one or more therapeutic agents by a dissolution mechanism,e.g., dissolution of a therapeutic agent contained in a solublecomponent of the coating into the medium in contact with the coating,e.g., tissue, in addition to a bioabsorption based transfer mechanism.As a result, the drug release mechanism can be based on the solubilityof the therapeutic agent in the surrounding medium. For example, atherapeutic agent near the interface between the hydrophobic coating andthe surrounding medium can experience a chemical potential gradientwhich can motivate the therapeutic agent out of the oil based coatingand into solution in the surrounding medium. Accordingly, in variousembodiments, the release of a therapeutic agent is not rate-limited bythe break-down or erosion of the coating, but is due to the enhancedbioabsorption of the therapeutic agent in the presence of lipophilic gelcomponents.

In various embodiments, the in vivo by-products of the hydrophobic,non-polymeric cross-linked gel convert into non-inflammatory byproducts,e.g., free fatty acids and glycerols, that themselves can release anddeliver one on or more of the therapeutic agents via a dissolutionmechanism.

Not to be limited by theory, in certain embodiments of the presentinvention, the components of the gel (such as fatty acids) may act as “acarrier” of the therapeutic agent directly into the cell and tissue asthe fatty acid groups become metabolized by the cell and cell membrane.In certain embodiments, it has been shown that the coating is drawn offthe medical device and absorbed nearly intact, in small fatty acidgroups with the therapeutic agent contained therein, without substantialrelease of the therapeutic agent into bodily fluids.

In one embodiment, the coating of the invention does not substantiallyrelease the therapeutic agent (e.g., into body fluids) but is directlytransferred to the local tissue that is in contact with the coating,e.g., through a physiochemical lipophillic attraction mechanism andsubsequent cell uptake of the fatty acid complex. Lipophillictransference and cell uptake may be controlled chemically by, forexample, adding uptake enhancers, varying the amount of curing, varyingdrug loading to alter viscosity, or other chemically modifying means, soas to modulated drug release into body fluids. Not to be limited bytheory, but the transference of the coating onto localized tissue maymaximize the drug distribution to the cells of the proximate tissue. Inaddition, this mechanism of transference and cell medicated uptake isbelieved not to induce substantial inflammation.

With the present invention, and in the field of soft tissueapplications, and in part because of the lipophilic mechanism enabled bythe bio-absorbable lipid based cross-linked gel of the presentinvention, the uptake of the therapeutic agent is facilitated by thedelivery of the therapeutic agent to the cell membrane by thebio-absorbable cross-linked gel. Further, the therapeutic agent is notfreely released into the body fluids, but rather, is delivered directlyto the cells and tissue. In prior configurations using polymer basedcoatings, the drugs were released at a rate regardless of the reactionor need for the drug on the part of the cells receiving the drug.

Therapeutic Agents

As utilized herein, the phrase “therapeutic agent(s)” refers to a numberof different drugs or agents available, as well as future agents thatmay be beneficial for use with the drug release coatings of the presentinvention, and may be used interchangeable with the term “drug.” Thetherapeutic agent component can take a number of different formsincluding anti-oxidants, anti-inflammatory agents, anti-coagulantagents, drugs to alter lipid metabolism, anti-proliferatives,anti-neoplastics, tissue growth stimulants, functional protein/factordelivery agents, anti-infective agents, anti-imaging agents, anestheticagents, therapeutic agents, tissue absorption enhancers, anti-adhesionagents, germicides, anti-septics, analgesics, prodrugs thereof, and anyadditional desired therapeutic agents such as those listed in Table 1below.

TABLE 1 CLASS EXAMPLES Antioxidants Alpha-tocopherol, lazaroid,probucol, phenolic antioxidant, resveretrol, AGI-1067, vitamin EAntihypertensive Agents Diltiazem, nifedipine, verapamilAntiinflammatory Agents Glucocorticoids (e.g. dexamethazone,methylprednisolone), leflunomide, NSAIDS, ibuprofen, acetaminophen,hydrocortizone acetate, hydrocortizone sodium phosphate,macrophage-targeted bisphosphonates Growth Factor AntagonistsAngiopeptin, trapidil, suramin Antiplatelet Agents Aspirin,dipyridamole, ticlopidine, clopidogrel, GP IIb/IIIa inhibitors, abcximabAnticoagulant Agents Bivalirudin, heparin (low molecular weight andunfractionated), wafarin, hirudin, enoxaparin, citrate ThrombolyticAgents Alteplase, reteplase, streptase, urokinase, TPA, citrate Drugs toAlter Lipid Fluvastatin, colestipol, lovastatin, atorvastatin,amlopidine Metabolism (e.g. statins) ACE Inhibitors Elanapril,fosinopril, cilazapril Antihypertensive Agents Prazosin, doxazosinAntiproliferatives and Cyclosporine, cochicine, mitomycin C, sirolimusAntineoplastics micophenonolic acid, rapamycin, everolimus, tacrolimus,paclitaxel, QP-2, actinomycin, estradiols, dexamethasone, methatrexate,cilostazol, prednisone, cyclosporine, doxorubicin, ranpirnas,troglitzon, valsarten, pemirolast, C-MYC antisense, angiopeptin,vincristine, PCNA ribozyme, 2-chloro- deoxyadenosine, mTOR targetingcompounds Tissue growth stimulants Bone morphogeneic protein, fibroblastgrowth factor Promotion of hollow organ Alcohol, surgical sealantpolymers, polyvinyl particles, 2-octyl occlusion or thrombosiscyanoacrylate, hydrogels, collagen, liposomes Functional Protein/FactorInsulin, human growth hormone, estradiols, nitric oxide, deliveryendothelial progenitor cell antibodies Second messenger targetingProtein kinase inhibitors Angiogenic Angiopoetin, VEGF Anti-AngiogenicEndostatin Inhibition of Protein Halofuginone, prolyl hydroxylaseinhibitors, C-proteinase Synthesis/ECM formation inhibitorsAntiinfective Agents Penicillin, gentamycin, adriamycin, cefazolin,amikacin, ceftazidime, tobramycin, levofloxacin, silver, copper,hydroxyapatite, vancomycin, ciprofloxacin, rifampin, mupirocin, RIP,kanamycin, brominated furonone, algae byproducts, bacitracin, oxacillin,nafcillin, floxacillin, clindamycin, cephradin, neomycin, methicillin,oxytetracycline hydrochloride, Selenium. Gene Delivery Genes for nitricoxide synthase, human growth hormone, antisense oligonucleotides LocalTissue perfusion Alcohol, H₂O, saline, fish oils, vegetable oils,liposomes Nitric oxide Donor NCX 4016 - nitric oxide donor derivative ofaspirin, SNAP Derivatives Gases Nitric oxide, compound solutions ImagingAgents Halogenated xanthenes, diatrizoate meglumine, diatrizoate sodiumAnesthetic Agents Lidocaine, benzocaine Descaling Agents Nitric acid,acetic acid, hypochlorite Anti-Fibrotic Agents Interferon gamma - 1b,Interluekin - 10 Immunosuppressive/Immuno Cyclosporine, rapamycin,mycophenolate motefil, leflunomide, modulatory Agents tacrolimus,tranilast, interferon gamma-1b, mizoribine, mTOR targeting compoundsChemotherapeutic Agents Doxorubicin, paclitaxel, tacrolimus, sirolimus,fludarabine, ranpirnase Tissue Absorption Enhancers Fish oil, squid oil,omega 3 fatty acids, vegetable oils, lipophilic and hydrophilicsolutions suitable for enhancing medication tissue absorption,distribution and permeation Anti-Adhesion Agents Hyaluronic acid, humanplasma derived surgical sealants, and agents comprised of hyaluronateand carboxymethylcellulose that are combined with dimethylaminopropyl,ethylcarbodimide, hydrochloride, PLA, PLGA Ribonucleases RanpirnaseGermicides Betadine, iodine, sliver nitrate, furan derivatives,nitrofurazone, benzalkonium chloride, benzoic acid, salicylic acid,hypochlorites, peroxides, thiosulfates, salicylanilide AntisepticsSelenium Analgesics Bupivicaine, naproxen, ibuprofen, acetylsalicylicacid

Some specific examples of therapeutic agents useful in theanti-restenosis realm include cerivastatin, cilostazol, fluvastatin,lovastatin, paclitaxel, pravastatin, rapamycin, a rapamycin carbohydratederivative (for example, as described in US Patent ApplicationPublication 2004/0235762), a rapamycin derivative (for example, asdescribed in U.S. Pat. No. 6,200,985), everolimus, seco-rapamycin,seco-everolimus, and simvastatin. With systemic administration, thetherapeutic agent is administered orally or intravenously to besystemically processed by the patient. However, there are drawbacks to asystemic delivery of a therapeutic agent, one of which is that thetherapeutic agent travels to all portions of the patient's body and canhave undesired effects at areas not targeted for treatment by thetherapeutic agent. Furthermore, large doses of the therapeutic agentonly amplify the undesired effects at non-target areas. As a result, theamount of therapeutic agent that results in application to a specifictargeted location in a patient may have to be reduced when administeredsystemically to reduce complications from toxicity resulting from ahigher dosage of the therapeutic agent.

The therapeutic agent component, as described herein, has some form oftherapeutic or biological effect. The oil component or oil compositioncomponent can also have a therapeutic or biological effect.Specifically, the cross-linked gel (and its oil constituents) enable thecells of body tissue of a patient to absorb the cross-linked gel 10itself, rather than breaking down the gel and disbursing by-products ofthe gel for ultimate elimination by the patient's body.

The term “mTOR targeting compound” refers to any compound whichmodulates mTOR directly or indirectly. An example of an “mTOR targetingcompound” is a compound that binds to FKBP 12 to form, e.g., a complex,which in turn inhibits phosphoinostide (PI)-3 kinase, that is, mTOR. Invarious embodiments, mTOR targeting compounds inhibit mTOR. SuitablemTOR targeting compounds include, for example, rapamycin and itsderivatives, analogs, prodrugs, esters and pharmaceutically acceptablesalts.

Calcineurin is a serine/threonine phospho-protein phosphatase and iscomposed of a catalytic (calcineurin A) and regulatory (calcineurin B)subunit (about 60 and about 18 kDa, respectively). In mammals, threedistinct genes (A-alpha, A-beta, A-gamma) for the catalytic subunit havebeen characterized, each of which can undergo alternative splicing toyield additional variants. Although mRNA for all three genes appears tobe expressed in most tissues, two isoforms (A-alpha and A-beta) are mostpredominant in brain.

The calcineurin signaling pathway is involved in immune response as wellas apoptosis induction by glutamate excitotoxicity in neuronal cells.Low enzymatic levels of calcineurin have been associated withAlzheimer's disease. In the heart or in the brain calcineurin also playsa key role in the stress response after hypoxia or ischemia.

Substances which are able to block the calcineurin signal pathway can besuitable therapeutic agents for the present invention. Examples of suchtherapeutic agents include, but are not limited to, FK506, tacrolimus,cyclosporin and include derivatives, analogs, esters, prodrugs,pharmaceutically acceptably salts thereof, and conjugates thereof whichhave or whose metabolic products have the same mechanism of action.Further examples of cyclosporin include, but are not limited to,naturally occurring and non-natural cyclosporins prepared by total- orsemi-synthetic means or by the application of modified culturetechniques. The class comprising cyclosporins includes, for example, thenaturally occurring Cyclosporins A through Z, as well as variousnon-natural cyclosporin derivatives, artificial or synthetic cyclosporinderivatives. Artificial or synthetic cyclosporins can includedihydrocyclosporins, derivatized cyclosporins, and cyclosporins in whichvariant amino acids are incorporated at specific positions within thepeptide sequence, for example, dihydro-cyclosporin D.

In various embodiments, the therapeutic agent comprises one or more of amTOR targeting compound and a calcineurin inhibitor. In variousembodiments, the mTOR targeting compound is a rapamycin or a derivative,analog, ester, prodrug, pharmaceutically acceptably salts thereof, orconjugate thereof which has or whose metabolic products have the samemechanism of action. In various embodiments, the calcineurin inhibitoris a compound of Tacrolimus, or a derivative, analog, ester, prodrug,pharmaceutically acceptably salts thereof, or conjugate thereof whichhas or whose metabolic products have the same mechanism of action or acompound of Cyclosporin or a derivative, analog, ester, prodrug,pharmaceutically acceptably salts thereof, or conjugate thereof whichhas or whose metabolic products have the same mechanism of action. Incertain embodiments, the therapeutic agents may cross link with the oilcontaining starting material. For example, therapeutic agents withunsaturations may cross link with the unsaturated fatty acids during thecuring process. The gels, coatings, medical devices, and methods of theinvention may comprise crosslinked fatty acids and therapeutic agents.Examples of therapeutic agents which may cross link includeanthracyclines, rapamycins, etc.

Therapeutically Effective Amounts and Dosage Levels

A therapeutically effective amount refers to that amount of a compoundsufficient to result in amelioration of symptoms, e.g., treatment,healing, prevention or amelioration of the relevant medical condition,or an increase in rate of treatment, healing, prevention or ameliorationof such conditions. When applied to an individual active ingredient,administered alone, a therapeutically effective amount refers to thatingredient alone. When applied to a combination, a therapeuticallyeffective amount can refer to combined amounts of the active ingredientsthat result in the therapeutic effect, whether administered incombination, serially or simultaneously. In various embodiments, whereformulations comprise two or more therapeutic agents, such formulationscan be described as a therapeutically effective amount of compound A forindication A and a therapeutically effective amount of compound B forindication B, such descriptions refer to amounts of A that have atherapeutic effect for indication A, but not necessarily indication B,and amounts of B that have a therapeutic effect for indication B, butnot necessarily indication A.

Actual dosage levels of the active ingredients in a coating of thepresent invention may be varied so as to obtain an amount of the activeingredients which is effective to achieve the desired therapeuticresponse without being unacceptably toxic. The selected dosage levelwill depend upon a variety of pharmacokinetic factors including theactivity of the particular therapeutic agent (drug) employed, or theester, salt or amide thereof, the mechanism of drug action, the time ofadministration, the drug release profile of the coating, the rate ofexcretion of the particular compounds being employed, the duration ofthe treatment, other drugs, compounds and/or materials used incombination with the particular compounds employed, and like factorsknown in the medical arts.

Other Agents

The coatings of the present inventions can also comprise one or moreother chemicals and entities in addition to the therapeutic agent,including, but not limited to, one or more of: a pharmaceuticallyacceptable carrier, an excipient, a surfactant, a binding agent, anadjuvant agent, and/or a stabilizing agent (including preservatives,buffers and antioxidants). The other agents can perform one or morefunctions, such as, e.g., an adjuvant may also serves as a stabilizingagent. In one embodiment, alpha-tocopherol TPGS is added to the coatingsof the present invention. The preservative can also be useful inaltering the physical properties of the oil component, as well asprotecting some of the beneficial properties of the oil component duringcertain curing processes. Such beneficial properties include the healingand anti-inflammatory characteristics previously mentioned.

In various embodiments, the coatings of the present invention includeone or more of a free radical scavenger and uptake enhancer. In variousembodiments, the coatings comprise vitamin E.

As previously stated, and in accordance with embodiments of the presentinvention, the cross-linked gel is formed of a naturally occurring oil,or composition including a naturally occurring oil, such as fish oil,cod liver oil, cranberry oil, and the like. A characteristic of thenaturally occurring oil is that the oil includes lipids, whichcontributes to the lipophilic action described later herein, that ishelpful in the delivery of therapeutic agents to the cells of the bodytissue. In addition, the naturally occurring oil can include theessential omega-3 fatty acids in accordance with several embodiments ofthe present invention.

It should be noted that as utilized herein to describe the presentinvention, the term vitamin E and the term alpha-tocopherol, areintended to refer to the same or substantially similar substance, suchthat they are interchangeable and the use of one includes an implicitreference to both. Further included in association with the term vitaminE are such variations including, but not limited to, one or more ofalpha-tocopherol, beta-tocopherol, delta-tocopherol, gamma-tocopherol,alpha-tocotrienol, beta-tocotrienol, delta-tocotrienol,gamma-tocotrienol, alpha-tocopherol acetate, beta-tocopherol acetate,gamma-tocopherol acetate, delta-tocopherol acetate, alpha-tocotrienolacetate, beta-tocotrienol acetate, delta-tocotrienol acetate,gamma-tocotrienol acetate, alpha-tocopherol succinate, beta-tocopherolsuccinate, gamma-tocopherol succinate, delta-tocopherol succinate,alpha-tocotrienol succinate, beta-tocotrienol succinate,delta-tocotrienol succinate, gamma-tocotrienol succinate, mixedtocopherols, vitamin E TPGS, derivatives, analogs and pharmaceuticallyacceptable salts thereof.

Compounds that move too rapidly through a tissue may not be effective inproviding a sufficiently concentrated dose in a region of interest.Conversely, compounds that do not migrate into a tissue may never reachthe region of interest. Cellular uptake enhancers such as fatty acidsand cellular uptake inhibitors such as alpha-tocopherol can be usedalone or in combination to provide an effective transport of a givencompound to a given region or location. Both fatty acids andalpha-tocopherol can be included in the drug release coatings of thepresent invention described herein. Accordingly, fatty acids andalpha-tocopherol can be combined in differing amounts and ratios tocontribute to a drug release coating in a manner that provides controlover the cellular uptake characteristics of the coating and anytherapeutic agents mixed therein.

For example, the amount of alpha-tocopherol can be varied in thecoating. Alpha-tocopherol is known to slow autoxidation in fish oil byreducing hydroperoxide formation, which results in a decrease in theamount of cross-linking in cured fish oil. In addition alpha-tocopherolcan be used to increase solubility of drugs in the fish oil forming thecoating. In various embodiments, alpha-tocopherol can actually protectthe therapeutic drug during curing, which increases the resulting drugload in the coating after curing. Furthermore, with certain therapeuticdrugs, the increase of alpha-tocopherol in the coating can serve to slowand extend drug release due to the increased solubility of the drug inthe alpha-tocopherol component of the coating. This, combined withalpha-tocopherol's ability to decrease cell membrane permeability,reflects the cellular uptake inhibitor functionality ofalpha-tocopherol, in that the delivery or uptake of the drug at thecellular level is slowed and extended over time.

Methods of Treating a Subject

The coatings, gels and medical devices of the present invention may beused to treat subjects. Examples of subjects include mammals, e.g.,humans. The subjects may be suffering from a disorder such as, forexample, vascular injury, soft tissue injury, or otherwise benefit fromthe use of one or more of the coatings, gels and/or medical devices ofthe invention.

In one embodiment, the invention pertains, at least in part, to a methodfor treating a subject. The method includes administering to the subjecta medical device with a coating such that the subject is treated,wherein the coating comprises a hydrophobic, non-polymeric cross-linkedgel, a fatty acid and a therapeutic agent.

In certain embodiments, the therapeutic agent is locally administered tothe subject. The term “local administration” refers to theadministration of the therapeutic agent generally to the tissueproximate to where the medical device is placed.

In another embodiment, the invention pertains to a method ofadministering a therapeutic agent to a target tissue in a subject. Themethod includes administering to the subject a hydrophobic,non-polymeric cross-linked gel and a therapeutic agent in proximity tothe target tissue; and allowing the therapeutic agent to be bioabsorbedinto the target tissue.

In another embodiment, the invention pertains, at least in part, to amethod of administering a therapeutic agent to a target tissue in asubject. The method includes administering to the subject a medicaldevice with a coating in proximity to the target tissue, wherein thecoating comprises a hydrophobic, non-polymeric cross-linked gel and atherapeutic agent; and allowing the therapeutic agent to be bioabsorbedinto the target tissue.

In a further embodiment, the therapeutic agent may be bioabsorbed bycellular uptake of the gel or coating. In another embodiment, the gelmay be bioabsorbed by cellular uptake of the coating. In anotherembodiment, the therapeutic agent may be bioabsorbed in the presence ofthe gel.

Curing and Gel Formation

Several methods are available to cure the natural oil starting materialcontaining one or more therapeutic agents to produce a non-polymericcross-linked gel coating for a drug release and delivery coating inaccordance with the present invention. Preferred methods for curing thestarting material to produce a hydrophobic non-polymeric cross-linkedgel coating of the present invention include, but are not limited to,heating (e.g., employing an oven, a broadband infrared (IR) lightsource, a coherent IR light source (e.g., laser), and combinationsthereof) and ultraviolet (UV) irradiation. The starting material may becross-linked through auto-oxidation.

Although some curing methods can have a have detrimental effects on atherapeutic agent combined with an omega-3 fatty acid oil startingmaterial, one characteristic that can remain after certain curing by,e.g., heating and UV irradiation methods is the non-inflammatoryresponse of the tissue when exposed to the cured omega-3 fatty acidmaterial. As such, an oil containing omega-3 fatty acids can be heated,UV irradiated, or both, for curing purposes, and still maintain some oreven a majority of the therapeutic effectiveness of the omega-3 fattyacids. In addition, although the therapeutic agent combined with theomega-3 fatty acid and cured with the omega-3 fatty acid can be renderedpartially ineffective, the portion remaining of the therapeutic agentcan, in accordance with the present invention, maintain pharmacologicalactivity and in some cases be more effective than an equivalent quantityof agent delivered with other coating materials.

In addition, some curing methods have been indicated to have detrimentaleffects on the therapeutic agent combined with the omega-3 fatty acid,making them partially or completely ineffective. As such, oils, and morespecifically oils containing omega-3 fatty acids, have been utilized asa delivery agent for the short term uncontrolled release of atherapeutic agent, so that minimal or no curing is required. However,there are no known uses of oils containing omega-3 fatty acids forcombination with a therapeutic agent in a controlled release applicationthat makes use of the therapeutic benefits of the omega-3 fatty acids.Further, some heating of the omega-3 fatty acids to cure the oil canlessen the total therapeutic effectiveness of the omega-3 fatty acids,but not eliminate the therapeutic effectiveness. One characteristic thatcan remain after certain curing by heating methods is thenon-inflammatory response of the tissue when exposed to the curedomega-3 fatty acid material. As such, an oil containing omega-3 fattyacids can be heated for curing purposes, and still maintain some or evena majority of the therapeutic effectiveness of the omega-3 fatty acids.In addition, although the therapeutic agent combined with the omega-3fatty acid and cured with the omega-3 fatty acid can be renderedpartially ineffective, the portion remaining of the therapeutic agentcan, in accordance with the present invention, maintain pharmacologicalactivity and in some cases be more effective than an equivalent quantityof agent delivered with other barrier or coating materials.

It should further be emphasized that the bio-absorbable nature of thecross-linked gel results in the cross-linked gel being completelyabsorbed over time by the cells of the body tissue. There are nosubstances in the cross-linked gel, or in vivo conversion by-products ofthe cross-linked gel, that induce an inflammatory response. Thecross-linked gel is generally composed of, or derived from, omega-3fatty acids bound to triglycerides, potentially also including a mixtureof free fatty acids and vitamin E compounds (alpha-tocopherol). Thetriglycerides are broken down by lipases (enzymes) which result in freefatty acids that can than be transported across cell membranes.Subsequently, fatty acid metabolism by the cell occurs to metabolize anysubstances originating with the cross-linked gel. The bio-absorbablenature of the cross-linked gel of the present invention results in thecross-linked gel being absorbed over time, leaving only an underlyingdelivery or other medical device structure that is biocompatible. Thereis no foreign body inflammatory response to the bio-absorbablecross-linked gel.

Although the present invention is bio-absorbable to the extent that thecross-linked gel experiences the uptake into or through body tissues, inthe specific embodiment described herein formed using naturallyoccurring oils, the exemplar oils are also lipid based oils. The lipidcontent of the oils provides a highly bio-absorbable cross-linked gel.More specifically, there is a phospholipids layer in each cell of thebody tissue. The fish oil, and equivalent oils, contain lipids as well.There is a lipophilic action that results where the lipids are attractedby each other in an effort to escape the aqueous environment surroundingthe lipids.

In accordance with various embodiments described herein, the coatingcomponent of the drug release coatings of the present invention isformed of a non-polymeric cross-linked gel, which can be derived fromfatty acid compounds. The fatty acids include omega-3 fatty acids whenthe oil utilized to form the coating is fish oil or an analog orderivative thereof. As liquid fish oil is heated, autoxidation occurswith the absorption of oxygen into the fish oil to create hydroperoxidesin an amount dependent upon the amount of unsaturated (C═C) sites in thefish oil. However, the (C═C) bonds are not consumed in the initialreaction. Concurrent with the formation of hydroperoxides is theisomerization of (C═C) double bonds from cis to trans in addition todouble bond conjugation. It has been demonstrated that hydroperoxideformation increases with temperature. Heating of the fish oil allows forcross-linking between the fish oil unsaturated chains using acombination of peroxide (C—O—O—C), ether (C—O—C), and hydrocarbon (C—C)bridges. The formation of the cross-links results in gelation of thecoating. The heating also can also result in the isomerization of cis(C═C) bonds into the trans configuration. The (C═C) bonds can also formC—C cross-linking bridges in the glyceride hydrocarbon chains using aDiels-Alder reaction. In addition to solidifying the coating throughcross-linking, both the hydroperoxide and (C═C) bonds can undergosecondary reactions converting them into lower molecular weightsecondary oxidation byproducts including aldehydes, ketones, alcohols,fatty acids, esters, lactones, ethers, and hydrocarbons.

UV initiated curing (photo-oxygenation) in accordance with the presentinvention involves the interaction between a double bond and singletoxygen produced from ordinary triplet oxygen by light and typically inthe presence of a sensitizer such as chlorophyll or methylene blue andresults in the formation of hydroperoxides. The chemical reaction isdescribed in the following graphic.

Since the above described reaction is not a radical chain process, itpossesses no induction period and is typically unaffected byantioxidants commonly used to inhibit autoxidation. However, thisreaction can be inhibited by single oxygen quenchers, such as carotene.This reaction is limited to C═C carbon atoms and results in a conversionfrom cis to trans C═C isomers during curing (as occurs with heatinitiated curing). However, photo-oxygenation using UV is a relativelyquicker reaction than autoxidation from heat curing, in the realm ofabout 1000-1500 times faster. The quicker reaction especially holds truefor methylene interrupted polyunsaturated fatty acids, such as EPA andDHA, which are found in the fish oil based embodiments of the presentinvention.

An important aspect of UV curing when compared to heat curing is thatalthough the byproducts obtained by both curing methods are similar,they are not necessarily identical in amount or chemical structure. Onereason for this is due to the ability of photo-oxygenation to createhydroperoxides at more possible C═C sites as shown for linolenate in thebelow graphic.

Photo-oxygenation, such as that which results from UV curing, due to itsenhanced ability to create inner hydroperoxides, also results in theability to form relatively greater amounts of cyclic byproducts, whichalso relates to peroxide cross-linking between fish oil hydrocarbonchains. For example, photo-oxygenation of linolenate results in 6different types of hydroperoxides to be formed, whereas autoxidationresults in only 4. The greater amount of hydroperoxides created usingphoto-oxygenation results in a similar, but slightly different,structure and amount of secondary byproducts to be formed relative toautoxidation from heat curing. Specifically, these byproducts arealdehydes, ketones, alcohols, fatty acids, esters, lactones, ethers, andhydrocarbons.

Schematic illustrations of various cross-linking mechanisms and schemesare shown in FIGS. 1-2.

Accordingly, in various embodiments, the drug release coating of thepresent inventions comprise a non-polymeric cross-linked gel derivedfrom fatty acid compounds, such as those of fish oil, that includes across-linked structure of triglyceride and fatty acid molecules inaddition to free and bound glycerol, monoglyceride, diglyceride, andtriglyceride, fatty acid, anhydride, lactone, aliphatic peroxide,aldehyde, and ketone molecules. It is believed that there are asubstantial amount of ester bonds remaining after curing in addition toperoxide linkages forming the majority of the cross-links in the gel.The coating degrades (e.g., by hydrolysis) into fatty acid, short andlong chain alcohol, and glyceride molecules, which are allnon-inflammatory and likewise can be consumable by cells, such as, e.g.,smooth muscle cells. Thus, the coating is bio-absorbable and degradesinto substantially non-inflammatory compounds. The amount of crosslinking may be modulated by adjusting the curing temperature, curingduration, amount of antioxidant, exposure to UV radiation or thepresence of a drying oil.

Coating Bioabsorption

The bio-absorbable nature of the coating component of the drug releasecoatings of preferred embodiments of the present inventions results inthe coating being completely absorbed over time by the cells of the bodytissue. In various embodiments, there are substantially no substances inthe coating, or in vivo conversion by-products of the coating whichinduce an inflammatory response, e.g., the coating converts in vivo intonon-inflammatory components. For example, in various embodiments, thecoatings of the present invention upon conversion do not produce lacticacid and glycolic acid break-down products in measurable amounts. Thepreferred coatings are generally composed of, or derived from, omega-3fatty acids bound to triglycerides, potentially also including a mixtureof free fatty acids and vitamin E (alpha-tocopherol). The triglyceridesare broken down by lipases (enzymes) which result in free fatty acidsthat can than be transported across cell membranes. For example, FIG. 3schematically depicts the base catalyzed hydrolysis of ester links in atrygliceride. Subsequently, fatty acid metabolism by the cell occurs tometabolize any substances originating with the coating. Thebio-absorbable nature of the coating of the present invention results inthe coating being absorbed over time, leaving only an underlyingdelivery or other medical device structure that is biocompatible. Thereis substantially no foreign body inflammatory response to thebio-absorbable coating or its break-downs products in the preferredembodiments of the present invention.

Tailoring of Drug and Delivery Profiles

In various aspects, the present invention provides methods of curing afish oil coating to provide a non-polymeric cross-linked gel coatingcontaining one or more therapeutic agents that can tailor the releaseand delivery profile of a therapeutic agent from the coating. Therelease profile can be tailored, e.g., through changes in oil coatingchemistry by varying coating composition, temperature, and cure times.The position of the drug-containing layer on the coated device providesan additional mechanism to alter the release profile of thenon-polymeric cross-linked gel coating. This can be achieved, e.g., byloading a drug into a cured base coating layer and coating a topcoatoverlayer cured coating onto the previously cured encapsulating baselayer.

An advantage of the cured fish oil coating in various embodiments of thepresent inventions is that the curing conditions utilized (i.e., curetime and temperature) can directly influence the amount of coatingcross-linking density and byproduct formation, which in turn effects thecoating bioabsorption. Thus, by altering the curing conditions employed,the release and delivery rate of a therapeutic compound of interestcontained in the coating can also be altered. Examples of curingconditions include exposure of the material to a temperature of about150-200° C. and/or ultra-violet light at a wavelength of about 254 nm.

In a various embodiments, an agent, such as, e.g., a free radicalscavenger, can be added to the starting material to tailor the drugrelease profile of the non-polymeric cross-linked gel that is formed. Invarious embodiments, vitamin E is added to the starting material to, forexample, to slow down autoxidation in fish oil by reducing hydroperoxideformation, which can result in a decrease in the amount of cross-linkingobserved in a cured fish oil coating. In addition, other agents can beused to increase the solubility of a therapeutic agent in the oilcomponent of the starting material, protect the drug from degradationduring the curing process, or both. For example vitamin E can also beused to increase the solubility of certain drugs in a fish oil startingmaterial, and thereby facilitate tailoring the drug load of the eventualcured coating. Thus, varying the amount of vitamin E present in thecoating provides an additional mechanism to alter the cross-linking andchemical composition of the non-polymeric cross-linked gel drug releaseand delivery coatings of the present invention.

In various embodiments, the present inventions provide coatings wherethe drug release profile of the coating is tailored through theprovision of two or more coatings and selection of the location of thetherapeutic agent. The drug location can be altered, e.g., by coating abare portion of a medical device with a first starting material andcreating a first cured coating, then coating at least a portion of thefirst cured coating with the drug-oil formulation to create a secondoverlayer coating. The first starting material can contain one or moretherapeutic agents. In various embodiments, the second overlayer coatingis also cured. The drug load, drug release profiles, and/or drugdelivery of the first coating, the overlay coating, or both, can betailored through the use of different curing conditions and/or additionof free radical scavengers (e.g., vitamin E), as described herein. Theprocess of providing two layers, can be extended to provide three ormore layers, wherein at least one of the layers comprises a hydrophobic,non-polymeric cross-linked gel. In addition, one or more of the layerscan be release and deliver a drug, and the drug release profile of suchlayers can be tailored using the methods described herein.

In various embodiments, the present inventions provide release anddelivery coatings where the drug release profile of the overall coatingis tailored through the provision of two or more coating regions withdifferent drug release profiles and selection of the location of thetherapeutic agent. In various embodiments, the formation of differentcoating regions with different drug release properties is obtained bylocation specific curing conditions, e.g., location specific UVirradiation, and/or location specific deposition of a starting materialon the coated device, e.g., by ink jet printing methods.

In an embodiment, the invention pertains, at least in part, to a methodfor tailoring a therapeutic agent release profile of a coating for amedical device. The method includes: combining the therapeutic agentwith an oil-containing starting material to form a second material;selecting a curing condition such that an effective amount of saidtherapeutic agent will be released and delivered in an appropriate timeperiod in vivo; and curing said second material according to said curingcondition, such that therapeutic release and delivery profile istailored. The method may further comprises the step of applying thesecond material to the medical device prior to curing.

The invention also pertains, at least in part, to a method for tailoringa therapeutic agent release profile of a coating for a medical device,by combining the therapeutic agent with an oil-containing startingmaterial to form a second material; selecting a release rate controllingamount of vitamin E, such that an effective amount of the therapeuticagent is released in an appropriate time period; combining the secondmaterial with the vitamin E to form a third material; and at leastpartially curing the third material, such the therapeutic release anddelivery profile is tailored. The method may further comprises the stepof applying the third material to the medical device prior to curing.

The term “release rate controlling amount” includes the amount ofVitamin E which is sufficient to modulate the release of the therapeuticagent. In a further embodiment, the therapeutic agent is added to amixture of about 1-20% vitamin E and 99-80% of a natural oil-containingstarting material.

In another embodiment, the invention also comprises a method fortailoring a therapeutic agent release and delivery profile of a coatingfor a medical device. The method includes selecting a first curingcondition; curing an oil-containing starting material according to thefirst curing condition to form a second material; combining thetherapeutic agent with an oil-containing starting material to form athird material; combining the third material with the second material toform a fourth material; selecting a second curing condition; and atleast partially curing the fourth material according to the secondcuring condition, such that therapeutic release and delivery profile istailored. The method may further comprises the step of applying thefourth material to the medical device prior to curing.

In yet another embodiment, the invention also pertains, at least inpart, to a method for tailoring a therapeutic agent release and deliveryprofile of a coating for a medical device. The method includes selectinga first curing condition; curing an oil-containing starting materialaccording to the first curing condition to form a second material;combining the therapeutic agent with about 1-20% vitamin E and about80-99% of a oil-containing starting material to form a third material;combining the third material with the second material to form a fourthmaterial; selecting a second curing condition; and at least partiallycuring the fourth material according to the second curing condition. Themethod may further comprises the step of applying the fourth material tothe medical device prior to curing.

In another embodiment, the invention pertains to a method for tailoringa therapeutic agent release and delivery profile of a coating for amedical device. The method includes curing an oil-containing startingmaterial to form a second material; combining said therapeutic agentwith an oil-containing starting material to form a third material;combining the third material with the second material to form a fourthmaterial; selecting a curing condition such that an effective amount ofthe therapeutic agent is released in an appropriate time period; andcuring the second material according to the curing condition.

In another embodiment, the invention pertains, at least in part, to amethod for tailoring a therapeutic agent release and delivery profile ofa coating for a medical device. The method includes curing a naturaloil-containing starting material to form a second material; combiningsaid therapeutic agent with 1-20% vitamin E and 99-80% of a naturaloil-containing starting material to form a third material; combining thethird material with the second material to form a fourth material;selecting a curing condition such that an effective amount of thetherapeutic agent is released and delivered in an appropriate timeperiod; and curing the second material according to the curingcondition.

Coating Approaches and Methods for Coating Medical Devices

The invention, also pertains, at least in part, to methods for coatingmedical devices. The medical devices may release therapeutic agents at adesired rate.

In an embodiment, the invention pertains, at least in part, to a methodfor producing a coating for a medical device with a desired delivery andrelease rate of a therapeutic agent. The method includes combining thetherapeutic agent with an oil-containing starting material to form asecond material; selecting a curing condition based on the desiredrelease rate; and curing the second material according to the selectedcuring condition, such that a desired drug delivery and release coatingis produced.

In another embodiment, the invention pertains, at least in part, to amethod for producing a coating for a medical device. The methodincludes: combining the therapeutic agent with an oil-containingstarting material to form a second material; selecting a release ratecontrolling amount of vitamin E based on the desired release rate;combining the second material with the release rate controlling amountof vitamin E to form a third material; and at least partially curing thethird material to form the coating.

In yet another embodiment, the invention also pertains to a method forproducing a coating for a medical device. The method includes selectinga first curing condition; curing an oil-containing starting materialaccording to the first curing condition to form a second material;combining the therapeutic agent with an oil-containing starting materialto form a third material; combining the third material with the secondmaterial to form a fourth material; selecting a second curing condition;and at least partially curing the fourth material according to thesecond curing condition.

In yet another embodiment, the invention also pertains to another methodfor producing a coating for a medical device. The method includes:selecting a first curing condition; curing a natural oil-containingstarting material according to the first curing condition to form asecond material; combining the therapeutic agent with about 1-20%vitamin E and about 80-99% of an oil-containing starting material toform a third material; combining the third material with the secondmaterial to form a fourth material; selecting a second curing condition;and at least partially curing the fourth material according to thesecond curing condition.

In another embodiment, the invention also pertains to a method forproducing a hydrophobic, non-polymeric cross-linked gel. The methodincludes combining a therapeutic agent with an oil-containing startingmaterial to form a second material; and at least partially curing thesecond material.

The methods of coating devices of the invention are further illustratedin the Figures. For example, FIG. 4 illustrates one method of making amedical device of the present invention, such as, e.g., a coated stent,in accordance with one embodiment of the present invention. The processinvolves providing a medical device, such as the stent (step 100). Acoating of a starting material, which is to form a hydrophobic,non-polymeric cross-linked gel coating, is then applied to the medicaldevice (step 102). One of ordinary skill in the art will appreciate thatthis basic method of application of a coating to a medical device, suchas a stent, can have a number of different variations falling within theprocess described. The step of applying a coating substance to form acoating on the medical device can include a number of differentapplication methods. For example, the medical device can be dipped intoa liquid solution of the coating substance. The coating substance can besprayed onto the device. Another application method is painting thecoating substance on to the medical device. One of ordinary skill in theart will appreciate that other methods, such as electrostatic adhesionand other application methods, can be utilized to apply the coatingsubstance to the medical device. Some application methods may beparticular to the coating substance and/or to the structure of themedical device receiving the coating. Accordingly, the present inventionis not limited to the specific embodiments of starting materialapplication described herein, but is intended to apply generally to theapplication of the starting material which is to become a hydrophobic,non-polymeric cross-linked gel coating of a medical device, takingwhatever precautions are necessary to make the resulting coatingmaintain desired characteristics.

FIG. 5 is a flowchart illustrating one example implementation of themethod of FIG. 4. In accordance with the steps illustrated in FIG. 5, abio-absorbable carrier component (e.g., a naturally occurring oil) isprovided along with a therapeutic agent component (step 110). Theprovision of the bio-absorbable carrier component and the provision ofthe therapeutic agent component can occur individually, or incombination, and can occur in any order or simultaneously. Thebio-absorbable carrier component is mixed with the therapeutic agentcomponent (or vice versa) to form a starting material which is to becomea hydrophobic, non-polymeric cross-linked gel coating (step 112). Thestarting material is applied to the medical device, such as the stent10, to form the coating (step 114). The coating is then cured (step 116)by any of the curing methods described herein to form a hydrophobic,non-polymeric cross-linked gel coating.

The coated medical device is then sterilized using any number ofdifferent sterilization processes (step 118). For example, sterilizationcan be implemented utilizing ethylene oxide, gamma radiation, E beam,steam, gas plasma, or vaporized hydrogen peroxide. One of ordinary skillin the art will appreciate that other sterilization processes can alsobe applied, and that those listed herein are merely examples ofsterilization processes that result in a sterilization of the coatedstent, preferably without having a detrimental effect on the coating 20.

It should be noted that the oil component or oil composition can beadded multiple times to create multiple tiers in forming the coating.For example, if a thicker coating is desired, additional tiers of theoil component or oil composition can be added after steps 100, 104, 106,108, 110, and/or 112. Different variations relating to when the oil iscured and when other substances are added to the oil are possible in anumber of different process configurations. Accordingly, the presentinvention is not limited to the specific sequence illustrated. Rather,different combinations of the basic steps illustrated are anticipated bythe present invention.

FIGS. 6A-6C illustrate some of the other forms of medical devicesmentioned above in combination with the coating 10 of the presentinvention. FIG. 6A shows a graft 50 with the coating 10 coupled oradhered thereto. FIG. 6B shows a catheter balloon 52 with the coating 10coupled or adhered thereto. FIG. 6C shows a stent 54 with the coating 10coupled or adhered thereto. Each of the medical devices illustrated, inaddition to others not specifically illustrated or discussed, can becombined with the coating 10 using the methods described herein, orvariations thereof. Accordingly, the present invention is not limited tothe example embodiments illustrated. Rather the embodiments illustratedare merely example implementations of the present invention.

Various aspects and embodiments of the present invention are furtherdescribed by way of the following Examples. The Examples are offered byway of illustration and not by way of limitation.

EXAMPLES

The following examples all employ a fish oil starting material. Thisstarting material contained a mixture of varying chain length saturatedand unsaturated fatty acids, glycerides, and triglycerides with aniodine value above 150 (a measure of the amount of chain unsaturation.The higher the iodine number, the more unsaturated the hydrocarbonchains. Specifically, the fish oil contained at least 18% of the all cisforms of 5,8,11,14,17-eicosapentaenoic acid (EPA) and 12% of the all cisforms of 4,7,10,13,16,19-docosahexaenoic acid (DHA) fatty acids. Thechemical structures of the fatty acid chains that were detected aftersaponification of the fish oil by GC/MS analysis provided in themanufacturer's certificate of analysis (Pronova, EPAX 3000 TG) arepresented in FIG. 7. The certificate of analysis also showed that thefish oil possessed 27.59% saturated fatty acids, 23.30% monounsaturatedfatty acids, and 45.05% polyunsaturated fatty acids, of which 40.63%were specifically omega-3 fatty acids.

In the various examples, the drug release coatings and tested coatedmedical devices were prepared generally as follows except as describedotherwise in the specific example. A coated medical device was preparedby encapsulating an either Atrium Prolite or Prolite Ultra polypropylenemesh in liquid fish oil (EPAX 3000 TG) using a manual dipping and/orroller application. The samples were subsequently placed on a Teflonlined metal pan and cured.

Example 1 Characterization of a Coating

In Example 1, the coated medical devices were cured in a high airflowoven at a range of times and temperatures (standard conditions were 150°F. for 3 days and 200° F. for 24 hours), after which the fish oil wasconverted into a cross-linked gel coating encapsulating thepolypropylene mesh by a lipid autoxidation mechanism using heat as acatalyst.

FTIR, DSC, liquid and solid state C¹³ NMR, X-ray diffraction, GC/MS, andLC/MS analysis were performed on the EPAX 3000 TG fish oil coatingscured at 200° F. for 24 hours.

FTIR Analysis: FIG. 8 is an FTIR analysis, which illustrates acomparison of the uncured fish oil (801) with the final cured coating.The FTIR shows that the coating contained hydroxyl (800), methylene(805), methyl (805), trans C═C (810), and anhydride/aliphaticperoxide/lactone bonds (815 and 830). A complex carbonyl band shape wasobtained and determined to contain ester (820), ketone (825), aldehyde(825), and fatty acid (800) byproduct absorptions in addition todetecting the presence of cross-linking as observed in theanhydride/lactone/aliphatic diacylperoxide band absorption. The positionof the methylene bands showed that the hydrocarbon chains present in thecoating were in a disordered state, which is consistent with anon-crystalline structure. Further, the cis C═C bonds in the fish oilstarting material (835) were observed to be almost entirely consumedduring the curing process. There was a corresponding increase in thetrans C═C bonds (810) during the curing process.

FTIR spectra were also acquired kinetically during the curing processusing a procedure described in the literature (see, e.g., Van de Voort,F. R.; Ismail, A. A.; Sedman, J.; and Emo, G. (1994) JAOCS, vol 70, no.3, pgs 243-253, the entire contents of which is hereby incorporated byreference) to monitor changes in the chemistry of the coating. FIG. 9Acompares the decrease of the normalized peak height of the cis bands andthe increase in the normalized peak heights of the trans C═C andanhydride/aliphatic peroxide/lactone C═O peak height during curing at200° C. FIG. 9C compares the normalized peak height changes in theoxidized byproduct (e.g., ketones, fatty acids and unsaturatedaldehydes) at 200° C. It was observed that initially during heating thatthe cis C═C bonds (♦ in FIG. 9A)(3011 cm⁻¹) were converted to isolatedand conjugated trans C═C bonds (▪ in FIG. 9A) (979 cm⁻¹) during thefirst 11 hours of curing. Concurrent with the conversion of the C═Cdouble bonds into the trans configuration was the appearance ofanhydride/aliphatic peroxide/lactone bonds and an almost maximalshifting of the C—O—C/C—O—O—C band (▴ in FIG. 9A), indicating theformation of cross-linking bonds, after which the coating solidifiedinto a sticky gel-like coating. After the initial gel solidificationprocess, continued curing of the coating resulted in partial consumptionof the trans C═C bonds in addition to the continued creation ofanhydride, lactone, aliphatic peroxide, ether, and peroxide cross-links,see. e.g., FIG. 1, (see, also, data of FIGS. 9A and 9C). The productionof shorter chain length fatty acid (▴), unsaturated aldehyde (•) andketone (X) byproducts were also monitored, shown in FIG. 9C. The coatingproduced at the end of the curing was a flexible gel-like coating thatmaintained a large number of ester bonds from the oil triglyceridestarting material.

Comparison of Coatings Cured at 150° F. and 200° F.

An additional comparison of the FTIR spectra of the fish oil cured at150° F. for 3 days with the 200° F. for 24 hours was performed. Thecomparison showed that curing at 150° F. for 3 days resulted in a 36%difference in the anhydride/aliphatic peroxide/lactone cross-linking, a25% difference in the trans C═C bonds and a 10% difference in the amountof fatty acid/ketone byproducts formed compared to the samples that werecured at 200° F. for 24 hours. These results indicated that the coatingscured at 200° F. were more cross-linked than the coatings cured at 150°F.

Further FTIR studies were performed in order to analyze the differencesbetween the coatings cured at 150° F. and 200° F. An amount of 125 μL ofOcean Nutrition fish oil was applied to 1×1″ polypropylene mesh andcured either at 200° F. for 24 hours or 150° F. for 3 days. Thedifferences between the coatings were determined using FTIR and thesaponification rate. The FTIR spectra of these different cured meshcoatings are presented in FIGS. 10A-10C. From a general inspection ofthe overall FTIR spectra of the 150 (1005) and 200° F. (1010) coatingscured on polypropylene mesh in FIG. 10A, there appears to be littlesignificant differences between the two coatings. However, upon zoomingin from 3600-2700 cm⁻¹ as illustrated in FIG. 10B, it can be seen thatthere are small differences in the OH band (1015), likely due to agreater amount of glycerides and fatty alcohols formed in the coatingcured at 150° F. (1005), when compared to the coating cured at 200° F.(1010). Additionally, inspection of the carbonyl band, as illustrated inFIG. 10C, showed approximately a 13% increase in absorption for thesample cured at 200° F. (1010) at approximately 1775 cm⁻¹, which isassigned to the formation of a combination of aliphatic peroxide,lactone, and anhydride cross-links (1020), when compared to the coatingcured at 150° F. (1005). Based on FTIR analysis, the coatings cured at150 and 200° F. are generally similar except for a few differences inbyproduct formation and cross-linking.

DSC: An extraction was performed in THF at 37° C. for 3 hours to isolatethe soluble and insoluble components of the fish oil coating cured ateither 150° F. for 3 days or 200° F. for 24 hours, followed byevaporation of the solvent in a hood and final drying in the bell jarvacuum. Weight measurements showed that this extraction of the coatingcured at 150° F. for 3 days resulted in a 62:38 ratio of soluble andinsoluble materials. The weight measurements showed that this extractionof the coating cured at 200° F. for 24 hours resulted in a 50:50 ratioof insoluble and soluble materials. DSC analysis of the insolublematerial of the coating cured at 150° F. for 3 days showed that theinsoluble material was 73% cured. A comparison analysis of DCS profilesof the soluble materials of the cured coatings indicates that thecoating cured at 200° F. possessed less long chain oxidized by productsthat the coating cured at 150° F.

A DSC profile of the soluble materials extracted from the coating curedat 200° F. for 24 hours is shown in FIGS. 11A. The DSC profile indicatesthat that the soluble materials are a polymorphous crystalline materialwith different molecular weight and chemical structures. FIG. 11B is aDSC profile of the insoluble materials obtained from the coating curedat 200° F. for 24 hours and indicates that the insoluble component is anamorphous material and that the apparent % cure of the insolublematerial is about 92%.

X-Ray Diffraction. X-ray diffraction results were inconclusive andsuggest the presence of a disordered, amorphous material as thistechnique is only sensitive to crystalline compounds. The result isconsistent with the FTIR and DSC analytical results.

C¹³ NMR Analysis: NMR confirmed the presence of C═C bonds, methyl,methylene, and C—O bonds of the C-QUR™ coating that resembled thestarting material, though with less absorption in the C═C area.

GC/MS and LC/MS: In preparation for GC/MS and LC/MS analysis, thecoating was dissolved in THF at about 65° C. and the soluble componentwas filtered away from the insoluble component. Using this process itwas determined that 68% of the coating was insoluble in THF andsuggested to be composed of a cross-linked fatty acid and glyceride fishoil cross-linked gel coating. The other 32% soluble portion of thecoating consisted of lower molecular weight compounds with a mass below3000. The soluble portion of the coating was determined to contain fattyacids and glycerides making up the majority of the soluble fraction witha small amount of ketones and aldehydes. A schematic of the molecularstructures of the components detected in the soluble fraction of thecoating is presented in FIG. 12. It should be noted that any alcoholbyproducts contained in the soluble component of the cured fish oilcoating would not be detected using these analytical methods.

Hydrolysis Testing

The experiments indicate that cured coatings of this example comprisemostly ester bonds in addition to lesser amounts of anhydride, lactone,and aliphatic peroxide bonds that will undergo hydrolysis in vivo toconvert into smaller components over time. The following observationssupport the conversion of the cured coating using a hydrolysismechanism, as shown in FIG. 3. These experiments, to assess theconversion of the cured coating, were conducted as follows.

A saponification reaction was performed in 0.1 M NaOH, pH>11 that isknown to readily convert triglyceride esters into lower molecular weightfatty acids and alcohols (i.e., glycerol). The cured fish oil coatingwas confirmed to degrade by a hydrolysis mechanism after being placed inthe NaOH solution and completely dissolved within 30 min, leaving barepolypropylene mesh behind.

To assess the differences in the degradation behavior of the coatingscured at 150° F. and 200° F., samples of the cured fish oil encapsulatedmesh samples were placed in a 0.1 M sodium phosphate buffer containing0.1 M NaCl solution at pH=7.4 at both 37° C. and 55° C. The coatingcured at 200° F. dissolved during an 18-day period at 55° C. whereas ittook 12 weeks to dissolve at 37° C. The coating cured at 150° F.dissolved during an 18-21 day period at 55° C.

To further assess the differences in the conversion behavior of thecoatings cured at 150° F. and 200° F., a 1×1″ coating was placed into a20 ml glass scintillation vial with 20 ml of 0.1 M NaOH, pH>11. Theamount of time for the coating to be hydrolyzed and be dissolved intosolution was determined to be approximately 14 minutes for the coatingcured at 150° F. and 19 minutes for the coatings cured at 200° F., whichcoincides with the FTIR spectral data where the coating cured at 200° F.was more cross-linked and thus took longer to saponify in basicconditions.

FTIR spectra acquired of the converted cured coating in buffer solutionwere consistent with the production of fatty acid, fatty acid salts, andalcohols. A representative spectrum acquired of the hydrolyzed materialat day 16 is shown in FIG. 13. This spectra illustrates significantdifferences in the OH (water and alcohols) band (1305), the CH₂ band(fatty acids and alcohols, 1310), the ester C═O band (1320) and thefatty acid C═O—O band (1325), when compared to the spectrum in FIG. 8.

Several tests were performed to determine the composition of theconverted material in 0.1 M phosphate buffer with 0.1 M sodium chlorideat 37 and 55° C. (1×1″ in 20 ml of buffer). The results of these testswere as follows.

HPLC Glyceride Test

No di- or triglyceride peaks were detected in the sample even afterconcentrating it by a factor of 5. However, peaks due to the presence offree fatty acids were assigned and a larger than normal solvent frontpeak was believed to be due to the presence of long chainedalcohols/glycerol. Results were similar the samples degraded in thebuffer at both 37 and 55° C.

GC Fatty Acid Profile

The sample for this test also had to be concentrated in order to obtainadequate detection by the GC. The fatty acids detected were C14, C16,C16-1, C18, and C18-1. The coating degraded at 55° C. had a greateramount of fatty acids detected than the coating degraded at 37° C., butin similar proportions.

HPLC Molecular Weight Test

The sample for this test also had to be concentrated by a factor of 5 inorder to obtain adequate detection. The weights detected for the sampledegraded at 55° C. (with normalized peak area %) indicated that 90% ofthe fraction of the sample soluble in THF had a molecular weight of lessthan or about equal to 1000. Likewise for the sample degraded at 37° C.,the weights and normalized peak areas indicated that 90% of the fractionof the sample soluble in THF had a molecular weight of less than orabout equal to 1000. The peak at 1000 would be due to structuresresembling triglycerides (although apparently too dilute to pick up onthe glyceride screen) and the components below 500 would be due to fattyacid or other lower molecular weight byproducts.

HPLC Glycerol Test

Several peaks attributed to fatty acids and alcohols were observed.Model cured fish oil films showed that the coating swelled at higher pHand temperature, which resulted in the coating to degrade more quickly.

Example 1 Summary

Based on the information provided from laboratory experiments,analytical data, and literature research a theoretical structure of thecured fish oil coating was derived, as schematically presented in FIG.14. Without being bound by a particular theory, the composition of theuncured coating (1305) is thought to be a mixture of saturated andpolysaturated (i.e., cis) fatty acid triglycerides. The partially curedcoating (1410) is thought to be composed of a flexible gel containingshort chain byproducts (i.e., fatty acids, ketones, aldehydes), lesspolyunsaturated fatty acids, (mostly trans C═C bonds), and cross-linkingof fatty acid chains (mostly peroxide, ether and C—C). The cured coating(1420) is believed to comprise short chain byproducts (i.e., fattyacids, ketones, aldehydes, and partially reacted fish oil, 1430), mostlysaturated fatty acids, with some monounsaturated fatty acids (all transC═C), and a network of cross-linked fatty acids and glycerides (1425)comprising mostly ester bonds with smaller amounts of peroxide, etherand C—C bonds. The cured coating comprises, then, a cross-linkedstructure of triglyceride and fatty acid molecules in addition to freeand bound glycerol, mono-, di-, and triglyceride, fatty acid, anhydride,lactone, aliphatic peroxide, aldehyde, and ketone molecules. There is alarge amount of ester bonds remaining after curing from the triglycerideoil headgroup in addition to cross-linking bands comprised of a mixtureof peroxide, ether and carbon-carbon linkages, but under the currentconditions of Example 1, the peroxide linkages appear to be dominant dueto the hydrolysable nature of the cured coating. Based on bench testing,the cured coating degrades into fatty acid, short and long chainalcohol, and glyceride molecules, which is consistent with hydrolyticdegradation of triglycerides (see, e.g., FIG. 3).

Example 2 Tailoring Drug Release Profile of Coating: Curing Conditions

An advantage of the cured fish oil coating in various embodiments of thepresent inventions is that the curing conditions utilized (i.e., curetime and temperature) can directly influence the amount of coatingcross-linking density and byproduct formation, which in turn effects therate of coating conversion to free fatty acids, fatty alcohols, andglycerol. The effects of various curing conditions on fish oil curingchemistry and drug release properties are demonstrated in this Example.

The Effects of Time and Temperature on the Release of Therapeutics

Drug delivery experiments were performed using coatings cured at 200° F.for 24 hours or at 150° F. for 3 days. All samples were 1×1″ anddissolution was performed in 0.01 M PBS solution. All drug samples wereloaded as an cured mesh coating created by mixing the liquid fish oiland drug together, with or without solvent, followed by coating a pieceof bare mesh and curing using either the 150 or 200° F. curingconditions.

Anti-Inflammatory Drug Delivery

FIG. 15 depicts the drug release profile measured for ananti-inflammatory drug. The figure compares two curing conditions,heating for 24 hours at 200° F. (♦) or 3 days at 150° F. (▴). Thestarting material comprised 2.4% model anti-inflammatory drug (after nMPsolvent was removed) in fish oil (EPAX 3000 TG). The initial drugloading after curing, based on HPLC measurements, was about 442 μg(14.84% recovery) for the 200° F. conditions, and about 238 μg (10.97%recovery) for the 150° F. conditions. It is to be noted that thepercentage amount recovered is dependent on the coating weight andamount of drug detected using HPLC methods after drug extraction fromthe cured fish oil coating.

These results show that the coating cured at 150° F., which has lesscross-linking and greater amount of soluble components, results in afaster drug release than the coating cured at 200° F., which possessmore cross-linking and fewer soluble components. This exampledemonstrates the ability to load an anti-inflammatory into cured fishoil coatings, and by using temperature to control the cross-linkingproperties of that coating, the drug release and delivery profile issignificantly altered.

Anti-Proliferative Drug Delivery

FIG. 16 depicts the drug release profile measured for ananti-proliferate drug. The figure compares two curing conditions,heating for 24 hours at 200° F. (♦) or heating for 3 days at 150° F.(▴). The starting material comprised 2.84% Cyclosporine A (CalBiochem)in fish oil (EPAX 3000 TG). No solvent was used as Cyclosporine A wassoluble in the fish oil with slight heating at 37° C. The initial drugloading after curing, based on HPLC measurements, was about 478 μg(14.22% recovery) for the 200° F. conditions, and about 1158 μg (26.00%recovery) for the 150° F. conditions. It is to be noted that thepercentage amount recovered is dependent on the coating weight andamount of drug detected using HPLC methods after drug extraction fromthe cured fish oil coating.

These results confirm that the coating cured at 150° F., which has lesscross-linking and greater amount of soluble components, results in afaster drug release than the coating cured at 200° F. cured coating,which possess more cross-linking and fewer soluble components. Thisexample demonstrates the ability to load an anti-proliferative,Cyclosporine A, into cured fish oil coatings and by using temperature tocontrol the cross-linking properties of the coating, the drug releaseand delivery profile is significantly altered.

Example 3 Tailoring Drug Release Profile of Coating: Other Agents

In various embodiments, the drug release and delivery profile of anon-polymeric cross-linked gel coating of the present invention can betailored by the inclusion of vitamin E in the starting material. VitaminE is an antioxidant known to slow down autoxidation in fish oil byreducing hydroperoxide formation, which results in a decrease in theamount of cross-linking observed in a cured fish oil coating. Inaddition, not all therapeutic compounds of interest present adequatesolubility in 100% fish oil and the vitamin E can be used to increasethe solubility of certain drugs in fish oil. Additionally, depending onthe chemical structure and properties of the drug to be loaded into thecoating, vitamin E may act to protect the drug during the curingprocess. These statements are supported in the following examples.

The Effects of Vitamin E Composition on Cured Fish Oil CoatingChemistry.

In this set of experiments, the curing conditions remained constant at150° F. for 3 days while the amount of vitamin E composition was variedfrom 0-5%. FTIR results showed that the amount of anhydride/aliphaticperoxide/lactone cross-linking decreased with increasing vitamin Ecomposition. In addition, the trans C═C bonds increased with increasingamounts of vitamin E. Comparison of the FTIR results are shown in FIG.17. The FTIR results show that by increasing the amount of vitamin E inthe coating that the fish oil component of the coating is lesscross-linked and cured than its 100% fish oil counter part.

The Ability of Vitamin E Composition to Protect a Therapeutic DuringCuring

Rapamycin loaded drug release mesh coatings (1×1″) were produced using150° F. curing for 3 days with varying amount of vitamin E present inthe cured fish oil coating. The amount of rapamycin loaded into all thecoating formulations before curing remained constant at 4.88%. Thepresence of the vitamin E acted to protect the rapamycin, as shown inthe extracted rapamycin (Rap) drug amounts recovered using HPLC analysisafter curing with varying amounts of vitamin E, as shown in Table 2.

TABLE 2 CURED COATING Rap Drug Loading % Rap Recovered (based Coating(HPLC) on HPLC) 100% Fish Oil 378 6.5 1% Vitamin E/Fish Oil 2126 34 2.5%Vitamin E/Fish Oil 2649 45 5% Vitamin E/Fish Oil 3013 52

These results show that increasing the amount of vitamin E increases theamount of rapamycin detected from the cured fish oil coating andindicates that vitamin E serves to protect the drug from oxidationduring curing. This also suggests that rapamycin (which has 3 conjugatedtrans C═C bands) might react with the polyunsaturated fatty acid chainsin the fish oil and likely cross-links with them during curing. VitaminE, which is a free-radical scavenger and can inhibit thecross-linking/oxidation of the fish oil, slows the kinetics of thecuring reaction and is believed to protect the rapamycin during thecuring process. The HPLC detection of rapamycin is directly dependent onthe preservation of the C═C bonds in the drug during curing; thus, theincreased detection of the rapamycin observed with increasing amounts ofvitamin E supports the theory that the vitamin E protects the drug bypreventing the oxidation of the drug C═C bonds.

The Ability of Vitamin E to Alter Release Profile

All coated mesh samples were 1×1″ and dissolution was performed in 0.01M PBS solution. All drug samples were loaded as an cured mesh coatingcreated by mixing the liquid fish oil and drug together, with or withoutsolvent, followed by coating a piece of bare mesh and curing at 150° F.for 3 days.

FIG. 18 depicts the drug release profile measured for rapamycin. Thefigure compares varying amounts of vitamin E added to the startingmaterial prior to curing for 3 days at 150° F. The starting materialscomprised 4.88% rapamycin (after solvent removal) in varying amounts ofvitamin E in fish oil coatings, with 100% fish oil and 378 μg loading ofrapamycin (♦), 1% vitamin E in fish oil and 2126 μg loading of rapamycin(▪), 2.5% vitamin E in fish oil and 2649 μg loading of rapamycin (X).The initial drug loading is shown in Table 2. It is to be noted that thepercentage amount recovered listed in Table 2 is dependent on thecoating weight and amount of drug detected using HPLC methods after drugextraction from the cured fish oil coating.

These results show that altering the vitamin E composition modifies therelease profile of a therapeutic agent from the cured fish oil coating.Increasing the amount of vitamin E results in lengthening and slowingthe release of the rapamycin into the dissolution buffer. Although theamount of rapamycin loaded in the initial coating formulation remainedconstant, increasing the amount of vitamin E in the coating results in,it is believed, protection of the drug and increasing the amount of freerapamycin extracted from the coating. Thus, despite the decrease incoating cross-linking and relative higher concentration of solublecomponents with increasing vitamin E content indicated by the FTIRresults, drug release and delivery is slow due to the increasedsolubility and affinity of the rapamycin for the vitamin E compared tothe aqueous release medium. Without being bound to any particulartheory, it is thought that rapamycin (which has 3 conjugated trans C═Cbands) reacts with the polyunsaturated fatty acid chains in the fish oiland likely cross-links with them during curing. The C═C bonds consumedduring the curing process would result in a loss of C═C band intensitythat is needed for the UV detection of rapamycin using the HPLC. VitaminE, which is a free-radical scavenger and can inhibit the cross-linkingof the fish oil, is believed to slow the kinetics of the curing reactionand as a result act to protect the rapamycin during the curing process.

Example 4 Tailoring Drug Release Profile of Coating: Multiple Coatingsand Drug Location

In various embodiments, the present inventions provide drug release anddelivery coatings where the drug release profile of the coating istailored through the provision of two or more coatings and selection ofthe location of the therapeutic agent. The chemistry of the variouscoating layers can be adjusted by employing different curing conditionsand/or vitamin E composition. The following examples demonstrate theability to alter the chemistry and position of the drug-containing layerin cured fish oil mesh coatings.

The Effects of Time, Temperature, and Position

All coated mesh samples were 1×1″ and dissolution was performed in 0.01M PBS solution. Drug release coated mesh samples were created by mixingthe fish oil and drug followed by coating a piece of bare mesh andcuring using either 150 or 200° F. curing conditions. Overlayer meshcoatings were created by applying a drug-fish oil coating onto apreviously coated and cured 100% fish oil coated mesh using 200° F.curing conditions, followed by curing the two coatings together ateither 150° F. for 3 days or 200° F. for 24 hours.

FIG. 19 depicts the drug release profile measured for ananti-inflammatory drug. The figure compares two curing conditions,heating for 24 hours at 200° F. or heating for 3 days at 150° F. and fordifferent positions of the drug (in the first layer versus in theoverlayer). The starting material comprised 3.29% modelanti-inflammatory drug (after nMP solvent was removed) in fish oil (EPAX3000 TG).

These results show that adjusting curing temperature and drug layercoating position can alter the release of an anti-inflammatory. Both thefirst coating layer (▴) and overlayer (X) samples cured at 150° F., dueto the lower amount of cross-linking, release more rapidly than the morecross-linked 200° F. samples. For the coatings cured at 150° F., theposition of the drug in the encapsulated coating results in a fasterrelease than for the overlayer coating. However, for the first coatinglayer (♦) and the overlayer coating (▪) samples at 200° F., the oppositeresulted. This illustrates the flexibility of the coating system wherethe release rate of the therapeutic from the overlayer and chemistry ofthe coating can be tailored based on the cure time, cure methods,thickness of coating, and/or temperature conditions employed.

FIG. 20 depicts a further drug release profile measured for ananti-inflammatory drug. The figure compares two curing conditions,heating for 24 hours at 200° F. or heating for 3 days at 150° F. and fordifferent positions of the drug (in the first layer versus in theoverlayer). The starting material comprised 2.4% model anti-inflammatorydrug (after nMP solvent was removed) in fish oil (EPAX 3000 TG). Theinitial drug loading after curing, based on HPLC measurements, was about793 μg (28.7% recovery, ▪) in the overlayer, and about 442 μg (14.84%recovery, ♦) in the first coating (underlayer) for the 200° F.conditions. The initial drug loading after curing, based on HPLCmeasurements, was about 477 μg (42.16% recovery, X) in the overlayer,and about 238 μg (10.97% recovery, ▴) in the first coating (underlayer)for the 150° F. conditions. It is to be noted that the percentage amountrecovered is dependent on the coating weight and amount of drug detectedusing HPLC methods after drug extraction from the cured fish oilcoating.

These results show that adjusting curing temperature and drug layercoating position altered the release of an anti-inflammatory, even at alower initial drug loading. Both the first layer and overlayer samplescured at 150° F., due to the lower amount of cross-linking, release morerapidly than the more cross-linked 200° F. samples. For the coatingscured at 150° F., the position of the drug in the first layer coatingresults in a faster dissolution than for the overlayer coating.

FIG. 21 depicts a further drug release profile measured for ananti-inflammatory drug. The figure shows data for curing by heating for24 hours at 200° F. and for different positions of the drug (in thefirst layer versus in the overlayer). The starting material comprised3.2% model anti-inflammatory drug (no nMP solvent used, theanti-inflammatory was suspended in the fish oil by vortexing) in fishoil (EPAX 3000 TG). The initial drug-oil dispersion looked cloudy andwas vortexed prior to coating samples in a metal weigh pan or the drugwould settle out. The initial drug loading after curing, based on HPLCmeasurements, was about 1348 μg (35.86% recovery, ▪) in the overlayer,and about 348 μg (9.19% recovery, ♦) in the first coating (underlayer).The coating had dissolved by day 27. It is to be noted that thepercentage amount recovered is dependent on the coating weight andamount of drug detected using HPLC methods after drug extraction fromthe cured fish oil coating.

These results show that adjusting drug layer coating position alters therelease of an anti-inflammatory, even without using a solvent tosolublize the drug in the coating.

FIG. 22 depicts a further drug release profile measured for ananti-proliferative. The figure compares two curing conditions, heatingfor 24 hours at 200° F. or heating for 3 days at 150° F. and fordifferent positions of the drug (in the first layer versus in theoverlayer). The starting material comprised 2.84% Cyclosporine A(CalBiochem) in fish oil (EPAX 3000 TG). No solvent was used asCyclosporine A was soluble in the fish oil with slight heating at 37° C.The initial drug loading after curing, based on HPLC measurements, wasabout 400 μg (12.9% recovery, ▪) in the overlayer, and about 478 μg(14.22% recovery, ♦) in the first coating (underlayer) for the 200° F.conditions. The initial drug loading after curing, based on HPLCmeasurements, was about 1536 μg (48.14% recovery, X) in the overlayer,and about 1158 μg (26.00% recovery, ▴) in the first coating (underlayer)for the 150° F. conditions. It is to be noted that the percentage amountrecovered is dependent on the coating weight and amount of drug detectedusing HPLC methods after drug extraction from the cured fish oilcoating.

These results show that adjusting curing temperature and drug layercoating position can also alter the release of Cyclosporine A, ananti-proliferative. Both the first layer (encapsulated) and overlayersamples cured at 150° F., due to the lower amount of cross-linking,release more rapidly than the more cross-linked samples cured at 200° F.For both the coatings cured at 150° F. or 200° F., the position of thedrug in the first coating results in a faster dissolution than for theoverlayer coating. Finally, the drug extraction results show that theCyclosporine A, which is a peptide, is more stable using the 150° F.curing conditions.

In Combination with Vitamin E

All coated mesh samples were 1×1″ and dissolution was performed in 0.01M PBS solution. All drug samples were loaded as an cured first layer onthe mesh and were created by mixing the liquid fish oil and drugtogether, with or without solvent, followed by coating a piece of baremesh and curing at 150° F. for 3 days.

FIG. 23 depicts the drug release profile measured for rapamycin. Thefigure compares varying amounts of vitamin E added to the startingmaterial prior to curing for 3 days at 150° F. The starting materialscomprised 4.88% rapamycin (after solvent removal) in varying amounts ofvitamin E in fish oil coatings (0-5%). The initial drug loading for the100% fish oil sample (no vitamin E) was after curing, based on HPLCmeasurements, was about 270 μg (5.5% recovery, •) in the overlayer, andabout 378 μg (16.5% recovery, ♦) in the first coating (underlayer). Theinitial drug loading for the 5% vitamin E in fish oil sample was aftercuring, based on HPLC measurements, was about 3584 μg (66.7% recovery,+) in the overlayer, and about 3013 μg (52.2% recovery, ▪) in the firstcoating (underlayer). It is to be noted that the percentage amountrecovered listed in Table 2 is dependent on the coating weight andamount of drug detected using HPLC methods after drug extraction fromthe cured fish oil coating.

These results show that altering the vitamin E composition can alter therelease of a therapeutic from the cured fish oil coating. Increasing theamount of vitamin E results in lengthening and slowing the release ofthe rapamycin into the dissolution buffer, due to its enhancedsolubility and affinity for the vitamin E component in the cured fishoil coating. Additionally, the cured 5% vitamin E/fish oil overlayercoating results in an increase in the amount of drug released whencompared to the encapsulated mesh.

Example 5 Heat Cured Encapsulated Mesh Coating Compared with a UV andHeat Cured Film Coating

A comparison of the FTIR spectra of a heat cured encapsulated meshcoating and a UV and heat cured film coating in FIGS. 24A and B. Anencapsulated mesh coating (2410) cured solely at 200° F. for 24 hourswas compared to a film (2405) that was first UV-cured for 15 minutes at254 nm followed by heat curing for 24 hours at 200° F. FIG. 24A presentsthe FTIR spectral band region from 3600-2700 cm⁻¹ and demonstrates thatthe OH band (2415) is greater for the cured film than the encapsulatedmesh due to the greater amount of glyceride, fatty alcohol and fattyacid byproducts formed in the film using the additional UV curing step.Inspection of the carbonyl band (FIG. 24B) illustrates an approximate24% increase in the cross-linking absorption at 1775 cm⁻¹ for the curedfilm coating when compared to the encapsulated mesh coating.Additionally, increased fatty acid absorption (2425) in the cured filmcoating is also observed. Thus, by FTIR analysis, the cured film coatingis more oxidized and cross-linked than the encapsulated mesh coatingusing the processing conditions described.

The effect of the amount of cross-linking on the ability for the filmand encapsulated mesh coatings to be hydrolyzed was tested using asaponification (i.e., hydrolysis of coating) test. The test wasperformed by placing a measured amount of the coating into a 20 ml glassscintillation vial with 20 ml of 0.1 M NaOH. The amount of time for thecoating to be hydrolyzed and be dissolved into solution was determinedto be approximately 18 minutes for the encapsulated mesh coating and 45minutes for the film, which coincides with the FTIR spectral data wherefilm was more cross-linked and thus took longer to saponify in basicconditions.

FTIR analysis (FIG. 25A and B) was also performed of the saponifiedcoating in solution after pH neutralization using HATR. The saponifiedsolution is clear at high pH (11) conditions, but becomes cloudy at a pHapproaching 7 due to the partial conversion of fatty acid salts toprotonated fatty acids. The solution was centrifuged and the supernatantfor each sample was removed for FTIR analysis. The pellet was washed andre-suspended in water twice prior to analysis. As can be seen from FIG.25A, the FTIR of the pellet for the film (2505) and the encapsulatedmesh coating (2510) are almost identical. FIG. 25B illustrates thatthere is only a slight difference in peak intensities between thesupernatant samples of the film (2515) and the encapsulated mesh (2520),which is believed to be a result of slight differences in the pHadjustment. Therefore, the FTIR data demonstrates that althoughdifferences in initial byproduct formation and cross-linking areobserved, the final chemistry is approximately the same and only thekinetics of the hydrolysis of the coating are affected.

Example 6 HPLC Dissolution for Cured Fish Oil Gels

An HPLC method was used to quantify drug dissolution in vitro. ASymmetry C8 (5 μm 4.6×250 mm) column with a mobile phase, 50%acetonitrile/50% (0.2% Acetic Acid) mobile phase and a 278 nm UVdetector was employed in this study. HPLC samples were prepared fordissolution with an acetonitrile diluent.

The drug release profiles for the cured fish oil coated stent werequantified with HPLC the above-described dissolution method. The HPLCresults are shown in FIGS. 26A-C. Overall, these experiments indicatedthat release drug profile could be controlled through adding an additive(e.g., TPGS), by the coating process, as well as the coating structures.

Additives

An additive, alpha-tocopherol polyethylene glycol—1000 Succinate (TPGS),was evaluated for the application for quick release of the rapamycincompound (FIG. 26A). A coating formulation was prepared with 11.8% TPGSand 41.2% of rapamycin compound along with a fish oil coating. Theformulation was applied to a stent and was uncured (♦), cured for 24hours at 93° C. (▪) or cured at 93° C. for 72 hours (▴). The coatedstents were then exposed to the dissolution conditions, and theresulting supernatant was analyzed by HPLC. The data shown in FIG. 26Aillustrates that the uncured coating released the rapamycin compoundmore quickly than the cured coatings and that the length of the curingwas an important factor in the drug release, as the coating cured for 72hours released the rapamycin compound slower than the coating cured for24 hours. In addition, this assay indicated that while TPGS was not aprimary antioxidant, but was a good surfactant.

Curing Time

FIG. 26B illustrates that cure time of the coating is an importantfactor in the drug release profile of the rapamycin compound. A seriesof stents were coated with a coating formulation containing 11.8%vitamin E and 41.2% of the rapamycin compound in the coating. The stentswere then cured at 93° C. for 0 hours (♦), 24 hours (▴), 48 hours (X) or72 hours (▪). The stents were then exposed to the dissolutionconditions, and the supernatant was analyzed by HPLC. The resultsindicate that there is an inverse correlation between the rate of drugrelease and the length of time of curing or cure time.

Thickness of Coating

FIG. 26C illustrates that the thickness and amount of the coating is animportant factor in the drug release profile of the rapamycin compound.A series of stents were coated with a fish oil formulations comprisingthe rapamycin compound in the amount of 106.1 μg (▴), 221.1 μg (♦),376.2 μg (▪) or 519.6 μg (X). The stents were then exposed to thedissolution conditions, and the supernatant was analyzed by HPLC. Theresults indicate that there is a direct correlation between the amountof coating applied to the medical device and the amount of the drugreleased.

Example 7 Sterilization of Cured Fish Gels

An MTT cell proliferation assay was performed on the pre-cured andpost-cured fish oil coating. The MTT test measures in vitro living ratsmooth muscle cells and the results were directly related to the numberof viable cultured cell lines. In this cell assay, the yellowtetrazolium salt (MTT) was reduced in metabolically active cells to forminsoluble purple formazan crystals, which were solubilized by theaddition of a detergent. The assay was used to quantify the activity ofthe rapamycin compound cured in various coating formulations on smoothmuscle cells using a fluorescent plate reader A linear relationshipbetween cell number and absorbance was established, which enabledquantification of changes in proliferation.

The MTT cell assay, the results of which are shown in FIG. 27, was usedto determine whether the cured fish oil coatings were stable tosterilization conditions. A series of stents were coated with a fish oilformulation comprising the rapamycin compound and were screened with theMTT cell assay for the % inhibitor of growth of the cells as a functionof the rapamycin concentration. The samples included a coating withoutthe rapamycin compound and sterilized by cold ETO gas (•), a coatingwith the rapamycin compound without sterilization (♦), a coating withthe rapamycin compound and sterilized before curing (▪) and a coatingwith the rapamycin compound and sterilized after curing (▴). Theseresults indicate that cured fish oil gel can be sterilized.

Example 8 FTIR Analysis of Implanted Coated Mesh Samples

This study was performed to assess the coating described herein afterimplantation in a rat abdominal wall defect for various lengths of time.Mesh samples were implanted in a rat abdominal wall defect for 4, 7, 14,21, and 28 days. At each timepoint, the entire piece of mesh and somesurrounding tissue was explanted, wrapped in saline soaked gauze andplaced in specimen containers. Sections of the explanted mesh (approx. 1cm×1 cm) were dissected, soaked in NERL water overnight in arefrigerator and air dried in a hood overnight. The dried mesh explantswere analyzed using the Micro-ATR accessory on both the rough (againstthe subcutaneous tissue) and smooth (against visceral tissue) sides inaddition to using HATR to analyze bulk sections of the coating.

FTIR analysis was performed on a bulk section of the coating using theHATR accessory to obtain a detailed chemical analysis of the coating.The HATR technique was better suited to determine a detailed chemicalanalysis on the implanted coating due to its ability to analyze agreater amount of the sample at one time, resulting from its increasedsampling area and IR beam penetration depth, when compared to theMicro-ATR technique. Since Micro-ATR analyzes a smaller area of thesample than the HATR with a 30% less IR beam penetration depth, coatinganalysis became problematic due to protein absorption on the surface ofthe device over time.

Physically, the explants were observed to have increased tissuein-growth on the rough side over time. This in-growth was very difficultto remove at the later time points (21 and 28 days). A very thin layerof tissue was noted over the smooth side of the explants at the latertime points (21 and 28 days). This layer of tissue was not attached tothe coating, but was lying on top of it and was easily removed. Inaddition, the coating appeared to dissolve over the course of the studyas indicated by a visible thinning of the coating where barepolypropylene fibers were exposed where they are normally buried on thecontinuous smooth side of the coating prior to implantation.

FIGS. 28A and B show the FTIR results for explanted coatings analyzedusing HATR at varying time points for the OH, NH, and CH₂ absorptionregions. The FTIR data shows a greater increase in protein integrationinto the coating with increasing implantation time as determined byincreases in the N—H (˜3285 cm⁻¹) (2805) and amide I vibrations (˜1645cm⁻¹) (2810) in FIG. 28A and FIG. 28B, respectively. These resultscorrelate with the physical observation of increased tissue in-growth onthe rough side of the mesh with increased implantation time, especiallyafter 21 days. Micro-ATR results confirmed this observation with greateramounts of protein absorption on the rough side (subcutaneous) whencompared to the smooth side (visceral).

The FTIR data also shows a time dependent conversion and absorption ofthe coating. Possible absorption and/or hydration of fatty acidbyproducts from the coating were initially observed in the shifting ofthe CH₂ band when comparing the T=0 spectrum, where fatty acidcrystallization (i.e., bloom) is detected at ˜2917 cm⁻¹ (2815), butnotably absent in the spectra at all other time points (FIG. 28C). Thisresult is more dramatically presented in the sharpening and shifting ofthe carbonyl band towards ˜1745 cm⁻¹ (FIG. 28D, 2820) as a function ofincreasing implantation time. The carbonyl band of the coating is broaddue to the combination of several functional group vibrations. Onecomponent of this band is due to the ester carbonyl vibrations of thepredominantly cross-linked glycerides (mono-, di-, and tri-) centered at˜1740 cm⁻¹, where the another component is due to the presence of mostlyfatty acid with some ketone and aldehyde byproducts from ˜1730-1700cm⁻¹. Thus, the shifting of the carbonyl band towards 1745 cm⁻¹ is aresult of absorption of the shorter chain length fattyacid/aldehyde/lketone byproducts in the coating by tissue in addition tobreaking down of the cross-linked glyceride component of the coating.The break down of the cross-linked glyceride component of the coating isconfirmed by the time-dependent decrease in the aliphaticperoxide/anhydride/lactone cross-linking band at ˜1780 cm⁻¹.

FIG. 29 shows the plot of the normalized changes in anhydride/aliphaticperoxide/lactone cross-linking (♦), glyceride ester (▪), fatty acid (▴),and protein (X) band peak height normalized to the CH₂ antisymmetricstretch as a function of time. This data numerically summarizes thechanges in peak height observed in the FTIR data discussed above. Theseresults show that the mesh coating is being broken down and absorbed invivo. Chemically, it appears that it is occurring by the absorption ofthe short chain fatty acid, ketone, and aldehyde byproducts in additionto the breaking down the aliphatic peroxide, anhydride, and lactonecross-linking bands. From literature studies on the metabolism oftriglycerides and fatty acids in the GI tract in vivo, we would expectthe shorter chain length byproducts to be absorbed more quickly than thecross-linked glyceride components. The FTIR data appears to beconsistent with this result. Without being bound by any particulartheory, based on the breakdown of the cross-linking bands and priorliterature, the FTIR data supports a hydrolysis and/or enzymatic (i.e.,lipase) degradation of the coating.

Numerous modifications and alternative embodiments of the presentinvention will be apparent to those skilled in the art in view of theforegoing description. Accordingly, this description is to be construedas illustrative only and is for the purpose of teaching those skilled inthe art the best mode for carrying out the present invention. Details ofthe structure may vary substantially without departing from the spiritof the invention, and exclusive use of all modifications that comewithin the scope of the appended claims is reserved. It is intended thatthe present invention be limited only to the extent required by theappended claims and the applicable rules of law.

All literature and similar material cited in this application,including, patents, patent applications, articles, books, treatises,dissertations and web pages, regardless of the format of such literatureand similar materials, are expressly incorporated by reference in theirentirety. In the event that one or more of the incorporated literatureand similar materials differs from or contradicts this application,including defined terms, term usage, described techniques, or the like,this application controls.

The section headings used herein are for organizational purposes onlyand are not to be construed as limiting the subject matter described inany way.

While the present inventions have been described in conjunction withvarious embodiments and examples, it is not intended that the presentteachings be limited to such embodiments or examples. On the contrary,the present inventions encompass various alternatives, modifications,and equivalents, as will be appreciated by those of skill in the art.

The claims should not be read as limited to the described order orelements unless stated to that effect. It should be understood thatvarious changes in form and detail may be made without departing fromthe scope of the appended claims. Therefore, all embodiments that comewithin the scope and spirit of the following claims and equivalentsthereto are claimed.

The invention claimed is:
 1. A coating for a medical device, whereinsaid coating comprises: a hydrophobic, non-polymeric cross-linked gel, atherapeutic agent, and fatty acids, said gel configured to release saidtherapeutic agent at a desired release rate in vivo; wherein saidnon-polymeric cross-linked gel is formed from one or more ofeicosapentaenoic acid (EPA) and docosahexanoic acid (DHA); and whereinsaid non-polymeric cross-linked gel comprises two or more of said fattyacids cross-linked directly to each other by one or more of lactonebonds or ester bonds.
 2. The coating of claim 1, wherein said coatinghas an average drug loading of about 500-1500 micrograms per square inchafter curing.
 3. The coating of claim 2, wherein said coating has anaverage drug loading of about 1100-1300 micrograms per square inch aftercuring.
 4. The coating of claim 2, wherein said coating releases saiddrug over a period of at least seven days.
 5. The coating of claim 2,wherein said coating releases said drug over a period of at leastfifteen days.
 6. The coating of claim 2, wherein said coating releasessaid drug over a period of about 17 to about 20 days.
 7. The coating ofclaim 1, wherein said coating has an average drug loading of about300-800 micrograms per square inch after curing.
 8. The coating of claim7, wherein said coating has an average drug loading of about 400-500micrograms per square inch after curing.
 9. The coating of claim 7,wherein said coating releases said drug over a period of at least twentydays.
 10. The coating of claim 7, wherein said coating releases saiddrug over a period of about 35 to about 45 days.
 11. The coating ofclaim 1, wherein said coating has an average drug loading of about150-350 micrograms per square inch after curing.
 12. The coating ofclaim 11, wherein said coating releases said drug over a period of atleast seven days.
 13. The coating of claim 11, wherein said coatingreleases said drug over a period of about 10 to about 15 days.
 14. Thecoating of claim 1, wherein said coating has an average drug loading ofabout 300-700 micrograms per square inch after curing.
 15. The coatingof claim 14, wherein said coating releases said drug over a period of atleast twenty days.
 16. The coating of claim 14, wherein said coatingreleases said drug over a period of about 25 to about 30 days.
 17. Ahydrophobic, non-polymeric cross-linked gel, wherein said gel comprisesa therapeutic agent and fatty acids; wherein said non-polymericcross-linked gel comprises two or more of said fatty acids cross-linkedto each other by one or more of lactone bonds or ester bonds; andwherein said non-polymeric cross-linked gel does not require the use ofexternal cross-linking agents.
 18. The gel of claim 17 wherein saidnon-polymeric cross-linked gel is formed from one or more ofeicosapentaenoic acid (EPA) and docosahexanoic acid (DHA).
 19. A coatingfor a medical device, wherein said coating comprises a hydrophobic,non-polymeric cross-linked gel, a therapeutic agent and fatty acids;wherein said non-polymeric cross-linked gel comprises athree-dimensional network of cross-linked fatty acids and glycerides;and wherein said fatty acids and glycerides are cross-linked directly toeach other by one or more of lactone bonds or ester bonds.